REVOLVING CREDIT
                             SECURED PROMISSORY NOTE
                                    ("Note")

$50,000,000.00                                                     March 1, 2000

FOR  VALUE  RECEIVED,   Mission  West  Properties,   L.P.,  a  Delaware  limited
partnership,  Mission West Properties,  L.P. I, a Delaware limited  partnership,
Mission West Properties  L.P. II, a Delaware  limited  partnership,  and Mission
West  Properties,   L.P.  III,  a  Delaware  limited  partnership  (collectively
"Borrower"),  promises  to pay to the order of Berg & Berg  Enterprises,  LLC, a
California limited liability company ("Lender") or its assigns, at 10050 Bandley
Drive, Cupertino, California 95014, or at such other place as the holder of this
Note may from time to time designate, the principal sum of Fifty Million Dollars
($50,000,000.00) (the "Credit Amount") or so much of that sum as may be advanced
under  this Note from time to time by any  holder,  plus  interest  as  computed
herein.

Interest on the principal sum of this Note from time to time outstanding will be
computed  from the date of each  advance of  principal  at LIBOR plus 1.30% (the
"Applicable  Interest Rate").  Interest will be computed on the basis of a three
hundred sixty (360) day year and the actual  number of days elapsed,  which will
result in the payment of more interest than if a 365-day year were used.

All accrued and unpaid  principal and interest shall be due and payable no later
than February 28, 2001.

Advances under this Note may be drawn by Borrower, up to the Credit Amount, upon
not less than 5 days notice to Lender.

Each payment shall be credited  first on the interest then due and the remainder
on the principal sum.

The undersigned  agrees that the holder of this Note may,  without notice to the
undersigned  and without  affecting  the  liability of the  undersigned,  accept
additional or substitute  security for this Note, or release any security or any
party liable for this Note, or extend or renew this Note.

If the  undersigned  consist of more than one person or entity,  their liability
and obligations under this Note will be joint and several.  Borrower jointly and
severally waives diligence,  presentment, protest and demand, notice of protest,
dishonor and  non-payment of this Note,  expressly  agrees that this Note or any
payment  hereunder,  may be  extended  from time to time,  and  consents  to the
acceptance of further security for this Note, including other types of security,
all without in any way affecting  the  liability of the  Borrower.  The right to
plead any and all  statutes  of  limitations  as a defense to any demand on this
Note, or on any guaranty hereof,  or to any agreement to pay the same, or to any
demand  secured by the Deed of Trust,  or other  security,  securing  this Note,
against Borrower,  the holder of any property encumbered by the Deed of Trust or
other  instrument  securing  this  Note,  and any  guarantors  or  sureties,  is
expressly waived by each and all said parties.

All amounts  payable  under this Note are payable in lawful  money of the United
States, free from any offset, deduction or counterclaim.  Checks will constitute
payment only when collected.

Upon any  default in the  payment of any amounts due under this Note or upon any
default under the Deed of Trust, the holder may, at its option and upon ten (10)
days' written notice to the undersigned, declare the entire unpaid principal sum
of this Note together with all accrued interest to be due and payable  provided,
however, that if the undersigned should cure such default under this Note or the
Deed of Trust within the time period described above, the right of the holder to
declare the entire  unpaid  principal sum of this Note together with all accrued
interest immediately due and payable shall terminate as to such default as if no
such default occurred.

The undersigned  agrees to pay all costs of collection when incurred,  including
but not  limited  to  reasonable  attorneys'  fees.  If any  suit or  action  is
instituted to enforce this Note, the undersigned promises to pay, in addition to
the costs and disbursements  otherwise allowed by law, such sum as the court may
adjudge as reasonable attorneys' fees in such suit or action.

This Note may be prepaid in whole or in part at any time without penalty.  Until
the maturity  date,  including all  extensions  thereof,  amounts  repaid may be
subsequently advanced under this Note, up to the Credit Amount.

This Note will be governed by the laws of the State of California.

This Note is a  non-recourse  loan secured by a Deed of Trust and  Assignment of
Rents (the "Deed of Trust")  executed by the  undersigned in favor of Lender and
covering  real  property  located  in San  Jose,  California.  The Deed of Trust
contains provisions for the acceleration of the maturity of this Note.

         Mission West Properties, L.P.,
         Mission West Properties, L.P. I,
         Mission West Properties, L.P. II, and
         Mission West Properties, L.P. III

           By: Mission West Properties, Inc., their general partner


               /s/ Carl E. Berg
               -----------------------------------------
               By: Carl E. Berg, President