EXHIBIT 5.1

[GRAY CARY WARE & FREIDENRICH LLP LETTERHEAD]

April 11, 2002

Securities and Exchange Commission
Judiciary Plaza
450 Fifth Street, N.W.
Washington, D.C. 20549

         Re:      Mattson Technology, Inc.
                  Registration Statement on Form S-3

Ladies and Gentlemen:

         As counsel to Mattson Technology, Inc., a Delaware corporation (the
"Company"), we are rendering this opinion in connection with the preparation and
filing of a registration statement on Form S-3 (the "Registration Statement")
relating to the registration under the Securities Act of 1933, as amended, of
7,423,644 shares of common stock which may be sold by the selling stockholders
named in the Registration Statement (the "Shares").

         We have examined all instruments, documents and records which we deemed
relevant and necessary for the basis of our opinion hereinafter expressed. In
such examination, we have assumed the genuineness of all signatures and the
authenticity of all documents submitted to us as originals and the conformity to
the originals of all documents submitted to us as copies.

         Based on such examination, we are of the opinion that the Shares
will, when issued, be duly authorized and validly issued, fully paid and
nonassessable.

         We hereby consent to the filing of this opinion as an exhibit to the
above-referenced Registration Statement and to the use of our name wherever it
appears in said Registration Statement, including the prospectus constituting a
part thereof, as originally filed or as subsequently amended.

                                          Respectfully submitted,

                                          /s/  Gray Cary Ware & Freidenrich LLP
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                                          GRAY CARY WARE & FREIDENRICH LLP