Exhibit 5.1

                [Letterhead of Wilson Sonsini Goodrich & Rosati]

                                September 3, 2003


Nanometrics Incorporated
1550 Buckeye Drive
Milpitas, CA 95035

                 Re: Nanometrics Incorporated Registration Statement on Form S-8

         Ladies and Gentlemen:

         We have examined the Registration  Statement on Form S-8 to be filed by
you with the Securities and Exchange Commission ("SEC") on or about September 3,
2003 (the  "Registration  Statement") in connection with the registration  under
the Securities  Act of 1933, as amended,  of up to 750,000 shares of your Common
Stock (the  "Shares")  reserved  for  issuance  under your 2003  Employee  Stock
Purchase  Plan  (the  "ESPP").  As your  legal  counsel,  we have  examined  the
proceedings taken and are familiar with the proceedings  proposed to be taken by
you in  connection  with the  issuance and sale of the Shares to be issued under
the ESPP.

         It is our  opinion  that,  upon  completion  of the  actions  being  or
contemplated  to be taken prior to the  issuance  of the Shares  pursuant to the
Registration  Statement  and the ESPP and upon  completion  of the actions being
taken in order to permit such  transactions to be carried out in accordance with
the securities laws of the various states,  where required,  such Shares will be
validly issued, fully paid and nonassessable.

         We consent to the use of this opinion as an exhibit to the Registration
Statement and further  consent to the use of our name wherever  appearing in the
Registration  Statement,  including the Prospectus  constituting a part thereof,
and any amendments thereto.

                                   Very truly yours,

                                   /s/ Wilson Sonsini Goodrich & Rosati

                                   WILSON SONSINI GOODRICH & ROSATI
                                   Professional Corporation