EXHIBIT 5.1
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          OPINION OF GREENBERG TRAURIG, LLP, COUNSEL TO THE REGISTRANT


                                                              September 27, 2005


Spire Corporation
One Patriots Park
Bedford, MA  01730-2396

        Re: Shares to be Issued Under the Spire Corporation 1996 Equity
Incentive Plan

Ladies and Gentlemen:

        We have assisted in the preparation of a Registration Statement on Form
S-8 (the "Registration Statement") to be filed with the Securities and Exchange
Commission (the "Commission") under the Securities Act of 1933, as amended (the
"Securities Act"), relating to 900,000 shares (the "Shares") of common stock,
$0.01 par value per share (the "Common Stock"), of Spire Corporation, a
Massachusetts corporation (the "Company"), that may be issued under the Spire
Corporation 1996 Equity Incentive Plan (the "Plan").

        We have examined the Articles of Organization and Bylaws of the Company,
each as amended and restated to date, and originals, or copies certified to our
satisfaction, of all pertinent records of the meetings of the directors and
stockholders of the Company, the Registration Statement and such other documents
relating to the Company as we have deemed material for the purposes of this
opinion.

        In our examination of the foregoing documents, we have assumed the
genuineness of all signatures, the authenticity of all documents submitted to us
as originals, the conformity to original documents of all documents submitted to
us as certified, photostatic or other copies, the authenticity of the originals
of any such documents and the legal competence of all signatories to such
documents.

        We assume that the appropriate action will be taken, prior to the offer
and sale of the Shares in accordance with the Plan, to register and qualify the
Shares for sale under all applicable state securities or "Blue Sky" laws.

        We express no opinion herein as to the laws of any state or jurisdiction
other than the state laws of The Commonwealth of Massachusetts and the federal
laws of the United States of America.

        It is understood that this opinion is to be used only in connection with
the offer and sale of the Shares while the Registration Statement is in effect.

        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.

        Based on the foregoing, we are of the opinion that the Shares have been
duly authorized for issuance and, when the Shares are issued and paid for in
accordance with the terms and conditions of the Plan, the Shares will be validly
issued, fully paid and nonassessable.

        We hereby consent to the filing of this opinion with the Commission in
connection with the Registration Statement in accordance with the requirements
of Item 601(b)(5) of Regulation S-K under the Securities Act. 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/ GREENBERG TRAURIG, LLP