1
                                                                    EXHIBIT 5.01

                          [FENWICK & WEST LLP LETTERHEAD]

                                 April 30, 1996


Integrated Systems, Inc.
201 Moffett Park Drive
Sunnyvale, CA  94089

Ladies and Gentlemen:

         At your request, we have examined the registration statement to be
filed by you with the Securities and Exchange Commission (the "Commission") on
April 30, 1996, pursuant to Rule 462(b) promulgated under the Securities Act of
1933, as amended (the "Securities Act") in connection with the registration
under the Securities Act of up to 115,000 shares of your Common Stock, 
(collectively, the "Shares"), all of which are presently issued and outstanding
or will be issued pursuant to the exercise of options and outstanding prior to
the date of the closing of the offering, and will be sold by certain selling
shareholders (the "Selling Shareholders"). Pursuant to Rule 462(b) such
registration statement is deemed to be a part of registration statement file
no. 333-02449 filed by you on April 12, 1996 (the two such registration
statements being collectively referred to herein as the "Registration
Statement"). All of the Shares are to be resold to the public by the
underwriters named in the Registration Statement.

         As your counsel, we have examined the proceedings taken by you in
connection with the issuance of up to 115,000 Shares that may be sold by the
Selling Shareholders.

         It is our opinion that the up to 115,000 Shares that may be sold by the
Selling Shareholders are, or upon the exercise of options, will be legally
issued, fully paid and nonassessable.

         We consent to the use of this opinion as an exhibit to the Registration
Statement and further consent to all references to us in the Registration
Statement, the Prospectus constituting a part thereof, and any amendments
thereto.

                                          Very truly yours,


                                          Fenwick & West