EXHIBIT 5.1

                                  February 7, 2000

Summit Design, Inc.
9305 S.W. Gemini Drive
Beaverton, Oregon 97008

    RE: REGISTRATION STATEMENT ON FORM S-4

Ladies and Gentlemen:

    We have examined the Registration Statement on Form S-4 filed by you with
the Securities and Exchange Commission on October 22, 1999 (Registration No.
333-89491), as amended (the "REGISTRATION STATEMENT"), in connection with the
registration under the Securities Act of 1933, as amended, of 16,268,288 shares
of your Common Stock, $0.01 par value per share (the "SHARES"). As your legal
counsel in connection with the transaction, we have examined the proceedings
taken and are familiar with the proceedings proposed to be taken by you in
connection with the sale and issuance of the Shares.

    It is our opinion that upon conclusion of the proceedings being taken or
contemplated by us, as your counsel, to be taken prior to the issuance of the
Shares, and upon completion of the proceedings being taken in order to permit
such transactions to be carried out in accordance with the securities laws of
the various states where required, the Shares, when issued in the manner
described in the Registration Statement, will be legally 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, including the joint proxy statement/prospectus
constituting a part thereof, and any amendment thereto.

                                          Very truly yours,
                                          WILSON SONSINI GOODRICH & ROSATI
                                          Professional Corporation
                                          /s/ WILSON SONSINI GOODRICH & ROSATI,
                                          P.C.