EXHIBIT 5.1

                                                    September 21, 1999

SUPERTEX, INC.
1235 Bordeaux Drive
Sunnyvale, CA 94088-3607

       Re: 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 on or about September 21,
1999 (the "Registration Statement"), in connection with the registration under
the Securities Act of 1933, as amended, of 900,000 shares of your Common
Stock (the "Shares") reserved for issuance under the 1991 Stock Option Plan,
(the "Plan").  As your legal counsel, we have examined the proceedings taken
and proposed to be taken in connection with the issuance, sale and payment of
consideration for the Shares to be issued under the Plan.

       It is our opinion that, when issued and sold in the manner referred to in
the Plan and pursuant to the agreements which accompany the Plan, the Shares
will be legally and validly issued, fully paid and non-assessable.

       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 and any amendments thereto.

                                   Very truly yours,

                                   WILSON,SONSINI, GOODRICH & ROSATI
                                   ProfessionalCorporation

                                   By: Thomas C. DeFilipps
                                       Thomas C.DeFilipps