EXHIBIT 5.1

July 22, 2011

NEXX Systems, Inc.

900 Middlesex Turnpike, Building #6

Billerica, Massachusetts 01821

RE:   Registration Statement on Form S-1

          File No. 333-164873

Ladies and Gentlemen:

This opinion is furnished to you in connection with a Registration Statement on Form S-1 (File No. 333-164873) (the “Registration Statement”) filed with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Securities Act”), for the registration of 8,050,000 shares of Common Stock, $0.001 par value per share (the “Shares”), of NEXX Systems, Inc., a Delaware corporation (the “Company”), including up to 1,050,000 Shares for which the underwriters have been granted an over-allotment option . The Shares are to be sold by the Company pursuant to the terms of an underwriting agreement (the “Underwriting Agreement”), which is referred to in the Registration Statement, between the Company and Needham & Company, LLC and Oppenheimer & Co., Inc., as representatives of the several underwriters named in the Underwriting Agreement, the form of which has been filed as Exhibit 1.1 to the Registration Statement.

We have examined the Registration Statement and such documents and records of the Company and other documents as we have deemed necessary for the purposes of this opinion. In such examination, we have assumed the following: (i) the authenticity of original documents and the genuineness of all signatures; (ii) the conformity to the originals of all documents submitted to us as copies and (iii) the truth, accuracy, and completeness of the information, representations, and warranties contained in the records, documents, instruments, and certificates we have reviewed. We express no opinion herein as to the laws of any state or jurisdiction other than the state laws of the Commonwealth of Massachusetts, the General Corporation Law of the State of Delaware and the federal laws of the United States of America.

Based upon the foregoing, we are of the opinion that the Shares to be issued and sold by the Company have been duly authorized for issuance and, when such Shares are issued and paid for in accordance with the terms and conditions of the Underwriting Agreement, such Shares will be validly issued, fully paid and nonassessable.

Please note that we are opining only as to the matters expressly set forth herein, and no opinion should be inferred as to any other matters. This opinion is based upon currently existing statutes, rules, regulations and judicial decisions, and we disclaim any obligation to advise you of

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July 22, 2011

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any change in any of these sources of law or subsequent legal or factual developments that might affect any matters or opinions set forth herein.

We hereby consent to the filing of this opinion with the Commission as an exhibit to the Registration Statement in accordance with the requirements of Item 601(b)(5) of Regulation S-K under the Securities Act and to the use of our name therein and in the related Prospectus under the caption “Legal Matters.” In giving such consent, we do not hereby admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission.

Very truly yours,

/s/ GENNARI ARONSON, LLP

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