FOURTH AMENDMENT TO LEASE


     THIS FOURTH AMENDMENT TO LEASE (this "Amendment") is made by and between
CHEVRON U.S.A. INC., a Pennsylvania corporation ("Landlord") and TEXAS
MICRO-SYSTEMS, INC., a Texas corporation ("Tenant"), made effective the 31st day
of July, 1995.

                                   WITNESSETH:

     WHEREAS, Landlord and Tenant did enter into that certain lease (the
"Lease") dated December 11, 1992, as amended effective February 24, 1993, and
October 28, 1993, and July 10, 1995, for certain leased space situated in the
Building known as 5959 Corporate Drive, Houston, Texas; and

     WHEREAS, Landlord and Tenant again desire to amend the Lease as set forth
herein;

     NOW THEREFORE, Landlord and Tenant in consideration of the premises and the
mutual benefits to be derived therefrom, do hereby covenant, stipulate and
agree, each with the other, to the following terms, covenants, conditions and
obligations as an amendment to the Lease:

     1.   All terms, covenants, obligations and conditions in this Amendment
          which conflict with a like provision in the Lease shall be controlling
          over and supersede any like provision in the Lease.

     2.   All terms, covenants, obligations and conditions in the Lease not
          superseded and/or amended by any provision in this Amendment shall
          remain in full force and effect. All defined terms in the Lease shall
          have the same meaning in this Amendment.

     3.   Article 1, Section 1.01 of the Lease is amended to include within the
          Premises approximately 283 square feet of Net Rentable Area located in
          the Northwest Quadrant of the first floor of the Building (the
          "Northwest Quadrant Space") as shown on Exhibit 1 attached hereto. The
          Premises shall also be increased to include 1,754 square feet of Net
          Rentable Area located in the Basement of the Building (the "Additional
          Basement Space") as shown on Exhibit 2 hereto.

     4.   The Base Rent is $8.50 per square foot of Net Rentable Area per annum
          for the Northwest Quadrant Space and $4.50 per square foot of Net
          Rentable Area per annum for the Additional Basement Space.

     5.   Tenant will take the Northwest Quadrant Space and Additional Basement
          Space "AS IS".




     Made as of the date first written above.

LANDLORD                                         TENANT

CHEVRON U.S.A. INC.                              TEXAS MICRO-SYSTEMS, INC.



By   GARY SCHUMAN                                By       MICHAEL STEWART
  ---------------------------------                -----------------------------
Its  Lease Manager                               Its      President and CEO
   --------------------------------                 ----------------------------




                                       2



                                                                       EXHIBIT 1



                        [Map of First Floor of Facility]







                                                                       EXHIBIT 2



                          [Map of Basement of Facility]