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Through and including              (the twenty-fifth day after the date of this prospectus), federal securities laws may require all dealers that effect transactions in these securities, whether or not participating in this offering, to deliver a prospectus. This requirement is in addition to the dealers’ obligation to deliver a prospectus when acting as underwriters and with respect to their unsold allotments or subscriptions.

“ES2” is a service mark of Rubicon Technology, Inc. This prospectus also includes other registered and unregistered service marks and trademarks of Rubicon Technology, Inc. and other persons.

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Risk factors

Investing in our common stock involves a high degree of risk. You should carefully consider the risks described below together with all of the other information contained in this prospectus, including the financial statements and the related notes appearing at the end of this prospectus, before making an investment decision. If any of the following risks or uncertainties actually occurs, our business, financial condition or operating results could materially suffer. In that event, the trading price of our common stock could decline and you may lose all or part of your investment.

RISKS RELATED TO OUR BUSINESS

We have incurred significant losses in prior periods and may incur losses in the future.

We have incurred significant losses in prior periods. In 2005 and 2006, we incurred net losses of $12.1 million and $7.6 million, respectively. As of September 30, 2007, we had an accumulated deficit of approximately $126.5 million. In addition, we expect our operating expenses to increase as we expand our business and become a public company. There can be no assurance that we will have sufficient revenue growth to offset increased expenses or to achieve profitability in future periods.

Our results of operations, financial condition and business will be harmed if we are unable to manage the expansion of our capacity effectively to meet customer demand.

We are in the process of significantly expanding our manufacturing capacity in order to meet current and anticipated customer demand. We are expanding by adding new equipment to our facilities in Franklin Park, Illinois, and we are planning to open a new facility in Bensenville, Illinois during the first quarter of 2008. Our capacity expansion involves significant risks, including the availability of capital equipment and the timing of its installation, availability and timing of required electric power, management of expansion costs, timing of production ramp, qualification of our new equipment and demands on management’s time. If our business does not grow fast enough to utilize this new capacity effectively, our business and financial results could be adversely affected. Conversely, delays in expanding our manufacturing capacity could impact our ability to meet future demand for our products. As a result, we might not be able to fulfill customer orders in a timely manner, which could adversely affect our customer relationships and operating results. Moreover, our efforts to increase our production capacity may not succeed in enabling us to manufacture the required quantities of our products in a timely manner or at the gross margins that we achieved in the past. There can be no assurance that we will be able to successfully reach our production, timing and cost goals for our expansion.

If LED lighting does not achieve greater market acceptance, or if alternative technologies are developed and gain market traction, prospects for our growth and profitability would be limited.

Our future success depends on increased market acceptance of LED lighting. Approximately 81% and 74% of our revenue was from sales of our products for use in the manufacture of LED products during 2006 and the first nine months of 2007, respectively. Potential customers for LED lighting systems may be reluctant to adopt LED lighting as an alternative to traditional lighting technology because of its higher initial cost and relatively low light output per unit in comparison with the most powerful traditional lighting devices. In addition, our potential customers may have substantial investments and know-how related to their existing lighting technologies, and may perceive risks relating to the novelty, complexity, reliability, quality, usefulness and cost-effectiveness of LED products when compared to other lighting sources available in the market. If acceptance of LED lighting does not increase significantly, then opportunities to increase our revenues and operate profitably would be limited.

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Moreover, if effective new sources of light other than LED devices are developed, our current products and technologies could become less competitive or obsolete. Any of these factors could have a material and adverse impact on our growth and profitability.

The technology used in the LED industry continues to change rapidly and if we are unable to modify our products to adapt to future changes in the LED industry, we will be unable to attract or retain customers.

We do not design or manufacture LEDs. Our ability to expand into new applications in the LED market depends on continued advancement in the design and manufacture of LEDs by others. The LED industry has been characterized by a rapid rate of development of new technologies and manufacturing processes, rapid changes in customer requirements, frequent product introductions and ongoing demands for greater functionality. Our future success will likely depend on our ability to develop new products for use in LED applications and to adjust our product specifications, such as our previous development of larger diameter wafers, in response to these developments in a timely manner. If our development efforts are not successful or are delayed, or if our newly developed products do not achieve market acceptance, we may be unable to attract or retain customers and our operating results could be harmed. In addition, although sapphire is currently the preferred substrate material for HB white, blue and green LED applications, we cannot assure you that the LED market will continue to demand the performance attributes of sapphire. Silicon carbide is another substrate material currently used for certain LED applications, including some that also use sapphire substrates. Other substrates being investigated and used in research and development for certain LED applications are aluminum nitride, zinc oxide and bulk gallium nitride. Research is also ongoing for the use of silicon substrates in LED applications. If sapphire is displaced as the substrate of choice for certain LED applications, our financial condition and results of operations would be materially and adversely affected unless we were able to successfully offer the competing substrate material.

Our continuing efforts to enhance our current products and to develop new products involve several risks, including:

If the development and acceptance of our products for the SOS RFIC market do not meet our expectations, our future operating results may be harmed.

The level of market acceptance of our SOS RFIC products will impact our future operating results. Our success in the SOS RFIC market depends on a number of factors, including:

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In addition, it is possible that other solutions, such as silicon-on-insulator, may become preferred over SOS. We cannot assure you that the RFIC market will continue to require the performance attributes of SOS solutions. If our products are not accepted more broadly in the RFIC market, our results of operations and business may be harmed.

The average selling prices of sapphire products have historically decreased over their life-cycles and continuing price decreases could adversely affect our results of operations.

Historically, our industry has experienced price decreases for a particular product over the life of that product. We anticipate that the average selling prices of our products may decrease in the future in response to competitive pricing pressures, increased sales discounts and new product introductions by our competitors. To lessen the effect of price decreases, we attempt to introduce new products as well as reduce manufacturing costs in order to maintain or improve our margins. However, if we are not able to successfully introduce new products or achieve these cost reductions in a timely manner, there could be a material adverse effect on our operating results and loss of market share.

We depend on a few customers for a major portion of our sales and our results of operations would be adversely impacted if they reduced their order volumes.

Historically, we have earned, and believe that in the future we will continue to earn, a substantial portion of our revenue from a small number of customers. In 2006, three customers accounted for 10% or more of our revenues and in the first nine months of 2007, three customers accounted for 10% or more of our revenues. In 2006, sales to Crystalwise Technology, Inc., Shinkosha Co., Ltd. and Tera Xtal Technology Corporation represented approximately 27%, 17% and 14% of our revenues, respectively, and in the first nine months of 2007, sales to Crystalwise, Shinkosha and Peregrine Semiconductor Corp. represented approximately 27%, 20% and 12% of our revenues, respectively. If we were to lose one of our major customers or have a major customer significantly reduce its volume of business with us, our revenues and profitability would be materially reduced unless we are able to replace such demand with other orders promptly. We expect to continue to be dependent on our significant customers, the number and identity of which may change from period to period.

We generally sell our products on the basis of purchase orders. We have agreements for longer-term purchase commitments from a few of our major customers; these commitments range from 12 months to 18 months. Those customers with whom we do not have longer-term purchase commitments could cease purchasing our products with little or no notice and without significant penalties. A number of factors could cause our customers to cancel or defer orders, including interruptions to their operations due to a downturn in their industries, natural disasters, delays in manufacturing their own product offerings into which our products are incorporated, securing other sources for the products that we manufacture or developing such products internally.

Our manufacturing processes may be interrupted or our production may be delayed if we cannot maintain sufficient electrical supply, which could adversely affect our business, financial condition and operating results.

Our manufacturing process requires a stable source of electricity. From time to time, we have experienced limited disruptions in our supply of electricity. Such disruptions, depending upon their duration, could result in a significant drop in throughput and yield of in-process crystal boules and create delays in our production. Although we use generators and other back-up sources of electricity, these replacement sources of electricity are only capable of providing effective back-up for limited periods of time. We cannot assure you that we will be successful in avoiding future disruptions in power or in mitigating the effects of such disruptions. Any material disruption in electrical supply could delay our production and could adversely affect our business, financial condition and operating results.

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Our gross margins and profitability may be adversely affected by rising energy costs.

The average cost of electricity increased significantly at the end of 2006 largely due to the deregulation of energy in the State of Illinois. Electricity prices could also increase due to overall changes to the price of energy due to conditions in the Middle East, natural gas shortages in the United States and other economic conditions and uncertainties regarding the outcome and implications of such events. If electricity prices continue to increase significantly, we may not be able to pass these price increases through to our customers on a timely basis, if at all, which could adversely affect our gross margins and results of operations.

We may not be able to effectively manage our growth, which could adversely affect our business, financial condition and operating results.

We have been experiencing a period of significant growth that has challenged, and will continue to challenge, our management and other resources. Our recent and anticipated growth has placed, and is expected to continue to place, significant strain on our research and development, sales and marketing, and operational and administrative resources. To manage our growth effectively, we must continue to:

We plan to spend substantial amounts of money to support our growth and may have additional unexpected costs. If we cannot attract a sufficient number of qualified people or manage growth effectively, our actual growth may be slower and could adversely affect our business, financial condition and operating results.

Our auditors have identified material weaknesses in our internal control over financial reporting. Our business and stock price may be adversely affected if we do not remediate these material weaknesses or if we have other material weaknesses in our internal controls. In addition, once we become subject to Section 404 of the Sarbanes-Oxley Act of 2002, investor confidence and our stock price could decline if we or our independent registered public accountants conclude that our internal control over financial reporting is ineffective.

Our independent registered public accounting firm issued a letter to our board of directors and management in which it identified certain matters that it considers to constitute material weaknesses in the design and operation of our internal control over financial reporting as of December 31, 2006. A “control deficiency” exists when the design or operation of a control does not allow management or employees, in the normal course of performing their assigned functions, to prevent or detect misstatements on a timely basis. A “significant deficiency” is a control deficiency, or combination of control deficiencies, that adversely affects the entity’s ability to initiate, authorize, record, process or report financial data reliably in accordance with accounting principles generally accepted in the US (“GAAP”) such that there is more than a remote likelihood that a misstatement of the entity’s financial statements that is more than inconsequential will not be prevented or detected by the entity’s internal control. Our auditors defined a “material weakness” as a significant deficiency, or combination of significant deficiencies, that results in more than a remote likelihood that a material misstatement of the financial statements will not be prevented or detected by the entity’s internal control.

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The material weaknesses identified by our auditors for the financial reporting period ending December 31, 2006 relate to the following:

In addition, our auditors noted several control deficiencies, which are of a lesser magnitude than the material weaknesses described above. These control deficiencies relate to our historical lack of a code of business conduct, our failure to have a process in place to receive, evaluate and retain complaints from our employees regarding questionable practices and our failure to document the process for reconciling our stock records with third party records. Our management and auditors were not required to, and did not, perform an evaluation of our internal control over financial reporting in accordance with Section 404 of the Sarbanes-Oxley Act of 2002. Had we and our auditors performed such an evaluation, additional material weaknesses and other control deficiencies may have been identified.

Because of these material weaknesses and control deficiencies, there is heightened risk that a material misstatement of our annual or quarterly financial statements will not be prevented or detected. While we have completed a number of our remediation efforts to address these material weaknesses, we cannot assure you that these remediation efforts have been entirely successful or that similar material weaknesses will not occur. Further, if we fail to take additional remediation efforts, we may fail to meet our future SEC reporting obligations, our financial statements may contain material misstatements and our operational results may be harmed.

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In addition, in connection with preparing the registration statement of which this prospectus is a part, we identified an error in our prior year financial statements. This error related to accounting for convertible debt with detachable warrants containing a beneficial conversion feature that was accounted for incorrectly. These errors resulted in the restatement of our previously issued 2004 and 2005 financial statements.

Once we become a public company, we will be required to comply with the requirements of Section 404 of the Sarbanes-Oxley Act of 2002. In this regard, beginning with our annual report on Form 10-K for the year ending December 31, 2008, we will be required on an annual basis to assess the effectiveness of our internal control over financial reporting and include a statement as to whether or not our internal control over financial reporting is effective. In addition, beginning with our year ending December 31, 2009, we will be required to have our independent registered public accounting firm issue an attestation report on our assessment of our internal control over financial reporting. In conducting our assessment, we will not be able to conclude that our internal control over financial reporting is effective if we have one or more material weaknesses. If we or our independent registered public accountants conclude that our internal control is not effective, our investors could lose confidence in our financial reports and our stock price could decline. An ineffective internal control environment could also adversely effect our ability to report our financial results in a timely manner and could materially adversely affect our business.

Our future operating results are expected to fluctuate significantly, which makes our future results difficult to predict and could cause our operating results for particular periods to fall below expectations.

Our revenues and operating results have fluctuated in the past and are likely to fluctuate in the future. These fluctuations are due to a number of factors, many of which are beyond our control. These factors include, among others:

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The foregoing factors are difficult to forecast, and these, as well as other factors, could materially adversely affect our quarterly or annual operating results. If our revenues or operating results fall below the expectations of investors or any securities analysts that may publish research on our company, the price of our common stock would likely decline.

Our gross margins could decline as a result of changes in our product mix and other factors, which may adversely impact our operating results.

We anticipate that our gross margins will fluctuate from period to period as a result of the mix of products that we sell in any given period, with our larger diameter sapphire products generally yielding higher gross margins than our smaller diameter products. If our sales mix shifts to lower margin products in future periods, our overall gross margin levels and operating results would be adversely impacted. Increased competition and the adoption of alternatives to our products, more complex engineering requirements, lower demand and other factors may lead to a further downward shift in our product margins, leading to price erosion and lower revenues for us in the future.

Our proprietary intellectual property rights may not adequately protect our products and technologies, and the failure to protect such rights could harm our competitive position and adversely affect our operating results.

To protect our technology, we have chosen to rely primarily on trade secrets rather than seeking protection through publicly filed patents. Trade secrets are inherently difficult to protect. While we believe we use reasonable efforts to protect our trade secrets, our directors, employees, consultants or contractors may unintentionally or willfully disclose our information to competitors, whether during or after the termination of their services to our company. If we were to seek to enforce a claim that a third-party had illegally obtained and was using our trade secrets, it would be expensive and time consuming, and the outcome would be unpredictable. In addition, courts outside the United States are sometimes less willing to protect trade secrets than US courts. Moreover, if our competitors independently develop equivalent knowledge, methods and know-how, it will be more difficult for us to protect our intellectual property and our business could be harmed.

We have no issued patents covering our products and technologies. Although we have filed applications for three patents, there can be no assurance that these patents will be issued or that any patents issued will be of significant value to our business. Our commercial success will depend on obtaining and maintaining trade secret, patent and other intellectual property protection of our products and technologies. We will only be able to protect products and technologies from unauthorized use by third parties to the extent that valid, protectable and enforceable trade secrets, patents or other intellectual property rights cover them.

If we are not able to defend the trade secret or patent protection positions of our products and technologies, then we may not be able to successfully compete with competitors developing or marketing competing products, and we may not generate enough revenue from product sales to justify the cost of development of our products and to achieve or maintain profitability.

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The protection of our intellectual property rights and the defense of claims of infringement against us by third parties may subject us to costly litigation.

Other companies might allege that we are infringing certain of their patents or other rights. If we are unable to resolve these matters satisfactorily, or to obtain licenses on acceptable terms, we may face litigation. Any litigation to enforce patents issued to us, to protect trade secrets or know-how possessed by us or to defend us or indemnify others against claimed infringement of the rights of others could have a material adverse effect on our financial condition and operating results. For example, one company has filed lawsuits against us and one of our executive officers alleging, among other things, misappropriation of trade secrets in connection with our employment of the executive officer, who was previously employed by the plaintiff. See “Business—Legal proceedings” for additional discussion of these lawsuits. Regardless of the validity or successful outcome of any such intellectual property claims, we may need to expend significant time and expense to protect our intellectual property rights or to defend against claims of infringement by third parties, which could have a material adverse effect on us. If we lose any such litigation where we are alleged to infringe the rights of others, we may be required to: pay substantial damages; seek licenses from others; or change, or stop manufacturing or selling, some or all of our products. Any of these outcomes could have an adverse effect on our business, results of operations or financial condition.

The markets in which we operate are very competitive, and many of our competitors and potential competitors are larger, more established and better capitalized than we are.

The markets for selling high-quality sapphire products are very competitive and have been characterized by rapid technological change. This competition could result in increased pricing pressure, reduced profit margins, increased sales and marketing expenses, and failure to increase, or the loss of, market share or expected market share, any of which would likely seriously harm our business, operating results and financial condition.

Some of our competitors and potential competitors are substantially larger and have greater financial, technical, marketing and other resources than we do. Given their capital resources, the large companies with whom we compete or may compete in the future, are in a better position to substantially increase their manufacturing capacity, research and development efforts or to withstand any significant reduction in orders by customers in our markets. Such larger companies typically have broader product lines and market focus and thus are not as susceptible to downturns in a particular market. In addition, some of our competitors have been in operation much longer than we have and therefore may have more long-standing and established relationships with our current and potential domestic and foreign customers.

We would be at a competitive disadvantage if our competitors bring their products to market earlier, if their products are more technologically capable than ours, or if any of our competitors’ products or technologies were to become preferred in the industry. Moreover, we cannot assure you that existing or potential customers will not develop their own products, or acquire companies with products, that are competitive with our products. Any of these competitive threats could have a material adverse effect on our business, operating results or financial condition.

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We are subject to risks from international sales that may harm our operating results.

In 2006 and the first nine months of 2007, revenues from international sales were approximately 89% and 78% of our total revenue. We expect that revenue from international sales will continue to constitute a significant portion of our total revenue for the foreseeable future. Our international sales are subject to a variety of risks, including risks arising from:

Our future success will depend on our ability to anticipate and effectively manage these and other risks associated with our international sales. Our failure to manage any of these risks could harm our operating results.

We are dependent on the continued services and performance of our senior management, the loss of any of whom could adversely affect our business, operating results and financial condition.

Our future success is dependent on the continued services and continuing contributions of our senior management who must work together effectively in order to design our products, expand our business, increase our revenues and improve our operating results. The loss of services of senior management, particularly Raja M Parvez, our president and chief executive officer, and Hap Hewes, our senior vice president sales and marketing, could significantly delay or prevent the achievement of our development and strategic objectives. In addition, key personnel may be distracted by activities unrelated to our business. We and Mr. Hewes are currently defendants in a lawsuit in which the plaintiff, a former employer of Mr. Hewes, is seeking a one-year prohibition on Mr. Hewes from competing with the plaintiff. See “Business—Legal proceedings” for additional discussion of this lawsuit. The loss of the services, or distraction, of our senior management for any reason could adversely affect our business, operating results and financial condition.

If we are unable to attract or retain qualified personnel, our business and product development efforts could be harmed.

Our success depends on our continued ability to identify, attract, hire, train, retain and motivate highly skilled technical, managerial, manufacturing, administrative and sales and marketing personnel. Competition for these individuals is intense, and we may not be able to successfully recruit, assimilate or retain sufficiently qualified personnel. In particular, we may encounter difficulties in recruiting and retaining a sufficient number of qualified technical personnel, which could harm our ability to develop new products and adversely impact our relationships with existing and future customers. The inability to

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attract and retain necessary technical, managerial, manufacturing, administrative and sales and marketing personnel could harm our ability to obtain new customers and develop new products and could adversely affect our business and operating results.

We rely on a limited number of suppliers for raw materials and key components.

We depend on a small number of suppliers for certain raw materials, components, services and equipment used in manufacturing our products, including key materials such as aluminum oxide and certain furnace components. We generally purchase these items with purchase orders, and we have no guaranteed supply arrangements with such suppliers. We are subject to variations in the cost of raw materials and consumables from period to period. We do not control the time and resources that these suppliers devote to our business, and we cannot be sure that these suppliers will perform their obligations to us or do so on a timely basis. In addition, some of these suppliers are located in regions of the world that may experience periods of political or economic instability.

Any significant delay in product delivery or other interruption or variation in supply from our key suppliers could prevent us from meeting demand for our products and from obtaining future business. If we were to lose key suppliers or our key suppliers were unable to support our demand, our manufacturing operations could be interrupted and we could be required to attempt to establish supply arrangements with other suppliers. In addition, the inability of our suppliers to support our demand could be indicative of a marketwide scarcity of the materials, which could result in even longer interruptions. Any such delay or interruption would impair our ability to meet our customers’ needs and therefore, could damage our customer relationships, and have a material adverse effect on our business and operating results.

Our products must meet exacting specifications, and undetected defects may occur, which may cause customers to return or stop buying our products.

Our customers establish demanding specifications for quality, performance, and reliability that our products must meet. While we inspect our products before shipment, they still may contain undetected defects. If defects occur in our products, we could experience lost revenue, increased costs, delays in, cancellations or rescheduling of orders or shipments, product returns or discounts or damage to our reputation, any of which would harm our operating results and our business. We have from time to time in the past experienced product quality, performance or reliability problems. For example, in 2005, before establishing our current manufacturing and quality control processes, we experienced a higher than expected rate of defects in our since discontinued two inch polished wafer product line, which led to an increase in the number and frequency of returns.

We may need to raise additional funding, which may not be available on favorable terms, if at all, or without substantial ownership dilution to our stockholders. If we do not raise any necessary funds, we may need to reduce certain aspects of our operations which could materially adversely affect our business prospects.

For the remainder of 2007, we expect to spend approximately $4.5 million for capital expenditures, primarily to increase our manufacturing infrastructure and capacity. We expect to spend between $12.0 million to $17.0 million per year for each of the next two years on capital expenditures to support our expected sales growth. We believe that the net proceeds from this offering, together with our existing cash, cash equivalents and investment balances, and interest income we earn on these balances, will be sufficient to meet our anticipated cash requirements for at least the next 12 months. However, we may need additional financing thereafter to execute on our current or future business strategies. We expect

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capital outlays and operating expenditures to increase over the next several years as we expand our infrastructure, manufacturing and research and development activities. The amount of additional capital we may need to raise depends on many factors, including:

We cannot be certain that additional capital will be available when and as needed or that our actual cash requirements will not be greater than anticipated. If we raise additional funds through the issuance of equity or convertible debt securities, the percentage ownership of our stockholders could be significantly diluted, and these newly-issued securities may have rights, preferences or privileges senior to those of existing stockholders. If we obtain additional debt financing, a substantial portion of our operating cash flow may be dedicated to the payment of principal and interest on such indebtedness, and the terms of the debt securities issued could impose significant restrictions on our operations. If we are unable to obtain financing on terms favorable to us, we may be unable to successfully execute our business plan.

We are subject to numerous environmental laws and regulations, which could expose us to environmental liabilities, increase our manufacturing and related compliance costs or otherwise adversely affect our business and operating results.

In our manufacturing process, we use water, oils, slurries, acids, adhesives and other industrial chemicals. We are subject to a variety of foreign, federal, state and local laws and regulations governing the protection of the environment. These environmental laws and regulations include those relating to the use, storage, handling, discharge, emission, disposal and reporting of toxic, volatile or otherwise hazardous materials used in our manufacturing processes. These materials may have been or could be released into the environment at properties currently or previously operated by us, at other locations during the transport of the materials, or at properties to which we send substances for treatment or disposal. If we were to violate or become liable under environmental laws and regulations or become non-compliant with permits required at some of our facilities, we could be held financially responsible and incur substantial costs, including investigation and cleanup costs, fines and civil or criminal sanctions, third-party property damage or personal injury claims. In addition, new laws and regulations or stricter enforcement of existing laws and regulations could give rise to additional compliance costs and liabilities.

Our operations are concentrated in a small number of nearby facilities, and the unavailability of one or more of these facilities could harm our business.

Our manufacturing, research and development, sales and marketing, and administrative activities are concentrated in our facilities in the Chicago metropolitan area. If, for any reason, including as a result of natural disaster, act of terrorism, war, outbreak of disease or other similar event, any of these facilities should be damaged or destroyed or become inaccessible or inoperable, our ability to conduct our business could be adversely affected or interrupted entirely.

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We may acquire other businesses, products or technologies; if we do, we may be unable to integrate them with our business effectively or at all, which may adversely affect our business, financial condition and operating results.

If we find appropriate opportunities, we may acquire complementary businesses, product lines or technologies. However, if we acquire a business, product line or technology, the process of integration may produce unforeseen operating difficulties and expenditures and may absorb significant attention of our management that would otherwise be available for the ongoing development of our business. Further, the acquisition of a business may result in the assumption of unknown liabilities or create risks with respect to our existing relationships with suppliers and customers. If we make acquisitions, we may issue shares of stock that dilute other stockholders, expend cash, incur debt, assume contingent liabilities or create additional expenses related to amortizing intangible assets, any of which may adversely affect our business, financial condition or operating results.

Changes in accounting standards issued by the Financial Accounting Standards Board or other standard setting bodies may adversely affect our financial condition and operating results.

Our financial statements are subject to the application of GAAP. From time to time, new accounting standards are issued or existing ones are revised by recognized authorities, including the Financial Accounting Standards Board. We may be required to adopt these new or revised accounting standards. It is possible that future accounting standards could change the current accounting treatment that we apply to our financial statements and such changes may adversely affect our financial condition and operating results.

RISKS RELATED TO OWNERSHIP OF OUR COMMON STOCK AND THIS OFFERING

Our common stock has not been publicly traded, and the price of our common stock may fluctuate substantially.

There has been no public market for our common stock before this offering. The initial public offering price of our common stock will be negotiated with the lead underwriters and the market price at which our common stock will trade following this offering will be determined by market forces. The investors who trade in our common stock may give different weight to factors or valuation methodologies or consider new factors or valuation methodologies other than those relied upon in determining our initial public offering price. Moreover, the price negotiated with the lead underwriters and the market price at which our common stock will trade following this offering may be lower than the historical per share value of our common stock. In addition, we cannot predict the extent to which a trading market will develop for our common stock or how liquid that market might become.

Factors related to our company and our business, as well as broad market and industry factors, may adversely affect the market price of our common stock, regardless of our actual operating performance. Factors that could cause fluctuations in our stock price include, among other things:

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Fluctuations caused by factors such as these may negatively affect the market price of our common stock. In addition, the other risks described elsewhere in this prospectus could adversely affect our stock price.

Management will have broad discretion for the use of proceeds from this offering, including the ability to apply the proceeds to uses that do not increase our operating results or market value.

We estimate that we will receive net proceeds of approximately $63.1 million from this offering. Assuming the underwriters exercise their overallotment option in full, we will receive net proceeds of approximately $75.2 million from this offering. These amounts assume an initial offering price of $13.00 per share, the midpoint of the initial public offering price range listed on the cover page of this prospectus. Approximately $7.5 million of such net proceeds will be used to repay existing indebtedness. Our management will have broad discretion in the use of the remaining net proceeds and may use these remaining net proceeds in ways that do not improve our operating results or market value or to which certain stockholders object. You will not have the opportunity, as part of your investment decision, to assess whether these remaining net proceeds are being used appropriately.

Future sales of substantial amounts of our common stock could adversely affect the price of our common stock.

If our stockholders sell substantial amounts of our common stock following this offering, the prevailing market price for our common stock could be adversely affected. Such sales by our stockholders might make it more difficult for us to issue new equity or equity-related securities in the future at a time and place we deem appropriate. Upon completion of this offering, based on the number of shares of common stock outstanding as of October 31, 2007 (assuming the conversion of all outstanding shares of our preferred stock into common stock and the net exercise of certain warrants immediately prior to the closing of this offering), we will have 19,391,387 shares of common stock outstanding. The 5,500,000 shares of common stock offered in this offering will be eligible for immediate resale in the public market without restrictions. The remaining 13,891,387 shares of common stock, which are currently held by our existing stockholders, may be sold in the public market in the future subject to the restrictions contained in Rule 144 under the Securities Act of 1933, as amended (the “Securities Act”). However, our stockholders, officers and directors, as well as each of the persons who will serve as our officers and directors upon the consummation of this offering, holding in the aggregate approximately 86% of our outstanding shares before giving effect to the offering have agreed with the underwriters that, without the prior written consent of the underwriters, they will not for a period of approximately six months from the closing of this offering, offer, sell, contract to sell, encumber, grant any option for the sale of or otherwise dispose of any of our securities. There are no agreements between the underwriters and any of our stockholders or affiliates releasing them from these lock-up agreements as of the date hereof. When the lock-up agreements expire or are terminated, approximately 12,332,082 shares of our common stock will be eligible for sale under Rule 144, Rule 144(d) or Rule 701 under the Securities Act. After the completion of this offering, the holders of an aggregate of approximately 12,201,629 shares of common stock will have registration rights. Following this offering, we intend to register all shares of common stock that we may issue under our stock option plans. Once we register these shares, they may be freely sold in the public market, subject to the lock-up restrictions described above, and subject, in the case of any awards under our stock-based compensation plans, to applicable vesting requirements.

You will experience immediate dilution in the book value of common stock purchased.

The initial public offering price per share is substantially higher than the net tangible book value per share of our outstanding common stock prior to the offering. Accordingly, if you purchase our common stock in this offering, you will incur immediate dilution of approximately $8.50 in the net tangible

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book value per share from the price you pay for our common stock, representing the difference between (i) the assumed initial public offering price of $13.00 per share (the midpoint of the estimated initial public offering price range set forth on the front cover of this prospectus) and (ii) the pro forma net tangible book value per share of $4.50 at September 30, 2007 after giving effect to this offering, which takes into account the $5.42 per share purchase price paid by our existing stockholders for their              shares of common stock. See “Dilution” in this prospectus for additional information.

Our board of directors does not intend to declare or pay any dividends to our stockholders in the foreseeable future.

The declaration, payment and amount of any future dividends will be made at the discretion of our board of directors, and will depend upon, among other things, the results of our operations, cash flows and financial condition, operating and capital requirements, and other factors the board of directors considers relevant. There is no plan to pay dividends in the foreseeable future, and if dividends are paid, there can be no assurance with respect to the amount of any such dividend.

We will incur increased costs and demands upon management as a result of complying with the laws and regulations affecting public companies, which could adversely affect our operating results.

We will be subject to the reporting requirements of the Securities and Exchange Commission (“SEC”) following the completion of this offering. As a public company we will incur significant legal, accounting and other expenses that we did not incur as a private company, including costs associated with public company reporting requirements. We also have incurred and will incur costs associated with corporate governance requirements, including requirements under the Sarbanes-Oxley Act, as well as rules implemented by the SEC and the NASDAQ Global Market. In addition, our management team will have to adapt to the requirements of being a public company. The expenses incurred by public companies generally for reporting and corporate governance purposes have been significant. We expect these rules and regulations to substantially increase our legal and financial compliance costs and to make some activities more time-consuming and costly. We are unable to currently estimate these costs with any degree of certainty. We also expect that these rules and regulations may make it more difficult and more expensive for us to obtain director and officer liability insurance, and we may be required to accept reduced policy limits and coverage or incur substantially higher costs to obtain the same or similar coverage than used to be available. As a result, it may be more difficult for us to attract and retain qualified individuals to serve on our board of directors or as our executive officers.

The concentration of our capital stock ownership with our directors and executive officers and their affiliates will limit your ability to influence corporate matters.

We anticipate that after the completion of this offering, our executive officers and directors and their affiliates will together own more than 61% of our outstanding capital stock and voting power. For the foreseeable future, they will have influence over our management and affairs and over all matters requiring stockholder approval, including the election of directors and significant corporate transactions, such as a merger or other sale of our company or our assets. Their ownership may limit your ability to influence corporate matters and, as a result, the market price of our common stock could be adversely affected.

We could be the subject of securities class action litigation due to future stock price volatility.

The stock market in general, and market prices for the securities of companies like ours, recently have experienced extreme volatility that often has been unrelated to the operating performance of the

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Risk factors

underlying companies. These broad market and industry fluctuations may adversely affect the market price of our common stock, regardless of our operating performance. When the market price of a stock declines significantly, holders of that stock have sometimes instituted securities class action litigation against the company that issued the stock. If any of our stockholders brought a lawsuit against us, our defense of the lawsuit could be costly and divert the time and attention of our management.

Our certificate of incorporation, bylaws and Delaware law may discourage takeovers and business combinations that our stockholders might consider in their best interests.

A number of provisions in our certificate of incorporation and bylaws, as well as anti-takeover provisions of Delaware law, may have the effect of delaying, deterring, preventing or rendering more difficult a change in control of Rubicon that our stockholders might consider in their best interests. These provisions include:

These provisions may prevent our stockholders from receiving the benefit from any premium to the market price of our common stock offered by a bidder in a takeover context. Even in the absence of a takeover attempt, the existence of these provisions may adversely affect the prevailing market price of our common stock if they are viewed as discouraging takeover attempts in the future.

The foregoing provisions of our certificate of incorporation and bylaws may also make it difficult for stockholders to replace or remove our management. These provisions may facilitate management entrenchment that may delay, deter, render more difficult or prevent a change in our control, which may not be in the best interests of our stockholders. See “Description of capital stock” for additional information on the anti-takeover measures applicable to us.

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Special note regarding forward-looking statements

This prospectus contains forward-looking statements that involve substantial risks and uncertainties. All statements, other than statements of historical facts, included in this prospectus regarding our future strategy, results of operations, financial position, net sales, projected costs, projected expenses, prospects and plans and objectives of management for future operations are forward-looking statements. We have based these forward-looking statements on our current expectations and projections about future events and financial trends that we believe may affect our financial condition, results of operations, business strategy, short-term and long-term business operations and objectives and financial needs. These forward looking statements can be identified by the use of terms and phrases such as “believe”, “plan”, “intend”, “anticipate”, “target”, “estimate”, “expect”, and the like, and/or future-tense or conditional constructions (“will”, “may”, “could”, “should”, etc.). Items contemplating or making assumptions about actual or potential future sales, market size and trends or operating results also constitute forward-looking statements.

Moreover, we operate in a very competitive and rapidly changing environment. New risks emerge from time to time. It is not possible for our management to predict all risks, nor can we assess the impact of all factors on our business or the extent to which any factor, or combination of factors, may cause actual results to differ materially from those contained in any forward-looking statements we may make. Before investing in our common stock, investors should be aware that the occurrence of the risks, uncertainties and events described in the section entitled “Risk factors” and elsewhere in this prospectus could have a material adverse effect on our business, results of operations and financial condition.

Although we believe that the expectations reflected in the forward-looking statements are reasonable, forward-looking statements are inherently subject to known and unknown risks, business, economic and other risks and uncertainties that may cause actual results to be materially different from those discussed in these forward-looking statements. Readers are urged not to place undue reliance on these forward-looking statements, which speak only as of the date of this prospectus. We assume no obligation to update any forward-looking statements in order to reflect any event or circumstance that may arise after the date of this prospectus, other than as may be required by applicable law or regulation. If one or more of these risks or uncertainties materialize, or if the underlying assumptions prove incorrect, our actual results may vary materially from those expected or projected.

This prospectus also contains statistical data and estimates, including those relating to market size and growth rates of the markets in which we participate, that we obtained from industry publications and reports generated by market research firms. These publications typically indicate that they have obtained their information from sources they believe to be reliable, but do not guarantee the accuracy and completeness of their information. Although we have assessed the information in the publications and found it to be reasonable and believe the publications are reliable, we have not independently verified their data.

You should read this prospectus and the documents that we reference in this prospectus and have filed with the SEC as exhibits to the registration statement, of which this prospectus is a part, with the understanding that our actual future results, levels of activity, performance and events and circumstances may be materially different from what we expect.

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Use of proceeds

We estimate that our net proceeds from the sale of the common stock we are offering hereby will be approximately $63.1 million, assuming an initial public offering price of $13.00 per share, which is the midpoint of the price range set forth on the cover of this prospectus, and after deducting underwriting discounts and commissions and estimated offering expenses that we must pay. We will not receive any proceeds from the sale of shares of common stock by the selling stockholders. If the underwriters exercise their overallotment option in full, we estimate that our net proceeds would be approximately $75.2 million, after deducting estimated underwriting discounts and commissions and estimated offering expenses that we must pay. Each $1.00 increase (decrease) in the assumed initial public offering price of $13.00 per share would increase (decrease) the net proceeds to us from this offering by approximately $5.1 million after deducting estimated underwriting discounts and commissions, assuming that the number of shares offered by us, as set forth on the cover page of this prospectus, remains the same. Depending on market conditions at the time of pricing of this offering and other considerations, we may sell fewer or more shares than the number set forth on the cover page of this prospectus.

The principal purposes of this offering are to obtain additional capital and to create a public market for our common stock. We intend to use a portion of the net proceeds of this offering to pay in full the principal and accrued interest outstanding under our loan and security agreement with Hercules Technology Growth Capital, Inc., dated as of April 9, 2007, which was approximately $6.1 million as of September 30, 2007. The loan and security agreement provides for a term loan in an aggregate principal amount of $12 million and a revolving credit facility in an aggregate principal amount of up to $4 million. The term loan bears interest at the prime rate (which was 8.25% as of September 30, 2007) plus 3.375%, and the revolving credit facility bears interest at the prime rate plus 0.25%. The term loan has a maturity date of December 31, 2010 and the revolving credit facility has a maturity date of April 1, 2008. There is no penalty for prepayment of the term loan. We used the proceeds of this loan for working capital, capital expenditures and other general corporate purposes. We expect to use the remaining net proceeds from this offering for working capital, capital expenditures and other general corporate purposes.

Until we use the net proceeds from this offering for the above purposes, we intend to invest the proceeds in short-term, investment-grade, interest-bearing securities.

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Dividend policy

We have never declared or paid cash dividends on our capital stock. We do not expect to pay any cash dividends in the foreseeable future. Any future determination to pay cash dividends will be made at the discretion of our board of directors, subject to applicable laws and compliance with contractual restrictions, and will depend on our results of operations, financial condition, future prospects and other factors our board of directors may deem relevant. Our amended and restated certificate of incorporation in effect immediately prior to this offering requires that all accrued but unpaid dividends on the outstanding shares of our preferred stock be fully paid prior to any payment of dividends to the holders of our common stock, unless otherwise approved by the holders of a majority of that series of preferred stock. In addition, it requires that any dividend declared on the shares of our common stock also be declared on the shares of our outstanding preferred stock on an as-converted to common stock basis. Upon the closing of this offering, all accrued but unpaid dividends on our outstanding preferred stock will convert into shares of our common stock.

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