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