EXHIBIT 4.3


                               [Face of Security]


THIS JUNIOR SUBORDINATED DEBENTURE IS A GLOBAL CERTIFICATE WITHIN THE MEANING 
OF THE INDENTURE HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF THE 
DEPOSITORY TRUST COMPANY (THE "DEPOSITARY") OR A NOMINEE OF THE DEPOSITARY.  
THIS JUNIOR SUBORDINATED DEBENTURE IS EXCHANGEABLE FOR JUNIOR SUBORDINATED 
DEBENTURES REGISTERED IN THE NAME OF A PERSON OTHER THAN THE DEPOSITARY OR 
ITS NOMINEE ONLY IN THE CIRCUMSTANCES DESCRIBED IN THE JUNIOR SUBORDINATED 
INDENTURE AND NO TRANSFER OF THIS JUNIOR SUBORDINATED DEBENTURE (OTHER THAN A 
TRANSFER OF THIS JUNIOR SUBORDINATED DEBENTURE AS A WHOLE BY THE DEPOSITARY 
TO A NOMINEE OF THE DEPOSITARY OR BY A NOMINEE OF THE DEPOSITARY TO THE 
DEPOSITARY OR ANOTHER NOMINEE OF THE DEPOSITARY) MAY BE REGISTERED EXCEPT IN 
LIMITED CIRCUMSTANCES.

UNLESS THIS JUNIOR SUBORDINATED DEBENTURE IS PRESENTED BY AN AUTHORIZED 
REPRESENTATIVE OF THE DEPOSITARY (55 WATER STREET, NEW YORK) TO SILICON 
VALLEY BANCSHARES OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR 
PAYMENT, AND ANY JUNIOR SUBORDINATED DEBENTURE ISSUED IS REGISTERED IN THE 
NAME OF CEDE & CO. OR SUCH OTHER NAME AS REQUESTED BY AN AUTHORIZED 
REPRESENTATIVE OF THE DEPOSITARY AND ANY PAYMENT HEREON IS MADE TO CEDE & 
CO., ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY A 
PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS 
AN INTEREST HEREIN.


                           SILICON VALLEY BANCSHARES

                    8.25% JUNIOR SUBORDINATED DEFERRABLE 
                    INTEREST DEBENTURE DUE JUNE 15, 2028

                            CUSIP NO.: 827064 AA 4


REGISTERED NO. 1              PRINCIPAL AMOUNT:  $41,237,125 


     Silicon Valley Bancshares, a corporation organized and existing under 
the laws of California (hereinafter called the "Company", which term includes 
any successor corporation under the Indenture hereinafter referred to), for 
value received, hereby promises to pay to Wilmington Trust Company, as 
Property Trustee, for the benefit of Cede & Co., as the nominee of the 
Depositary Trust Company and the registered owner of this Debenture, the 
principal sum of $41,237,125 on June 15, 2028; provided that the Company may 
shorten the Stated Maturity of the principal of this Security to a date not 
earlier than June 15, 2003.  The Company further promises to pay interest on 
said principal sum from the date of original issuance or from the most recent 
interest payment date (each such date, an "Interest Payment Date") on which 
interest has been paid or duly provided for, quarterly (subject to deferral 
as set forth herein) in arrears on the 



15th day of March, June, September and December of each year commencing 
September 15, 1998 at the rate of 8.25% per annum, until the principal hereof 
shall have become due and payable, plus Additional Interest, if any, until 
the principal hereof is paid or duly provided for or made available for 
payment and on any overdue principal and (without duplication and to the 
extent that payment of such interest is enforceable under applicable law) on 
any overdue installment of interest at the rate of 8.25% per annum, 
compounded quarterly.  The amount of interest payable for any period shall be 
computed on the basis of twelve 30-day months and a 360-day year.  The amount 
of interest payable for any partial period shall be computed on the basis of 
the number of days elapsed in a 360-day year of twelve 30-day months.  In the 
event that any date on which interest is payable on this Security is not a 
Business Day, then a payment of the interest payable on such date will be 
made on the next succeeding day which is a Business Day (and without any 
interest or other payment in respect of any such delay), with the same force 
and effect as if made on the date the payment was originally payable.  A 
"Business Day" shall mean any day other than a Saturday or Sunday or a day on 
which banking institutions in the State of California are authorized or 
required by law or executive order to remain closed or on a day on which the 
Corporate Trust Office of the Trustee, or the principal office of the 
Property Trustee under the Trust Agreement (hereinafter referred to) is 
closed for business.  The interest installment so payable, and punctually 
paid or duly provided for, on any Interest Payment Date will, as provided in 
the Indenture, be paid to the Person in whose name this Security (or one or 
more Predecessor Securities) is registered at the close of business on the 
Regular Record Date for such interest installment, which shall be the next 
Business Day preceding such Interest Payment Date.  Any such interest 
installment not so punctually paid or duly provided for shall forthwith cease 
to be payable to the Holder on such Regular Record Date and may either be 
paid to the Person in whose name this Security (or one or more Predecessor 
Securities) is registered at the close of business on a Special Record Date 
for the payment of such Defaulted Interest to be fixed by the Trustee, notice 
whereof shall be given to Holders of Securities of this series not less than 
10 days prior to such Special Record Date, or be paid at any time in any 
other lawful manner not inconsistent with the requirements of any securities 
exchange on which the Securities of this series may be listed, and upon such 
notice as may be required by such exchange, all as more fully provided in 
said Indenture.

     So long as no Event of Default has occurred and is continuing, the 
Company shall have the right at any time during the term of this Security to 
defer payment of interest on this Security, at any time or from time to time, 
for up to 20 consecutive quarterly interest payment periods with respect to 
each deferral period (each an "Extension Period"), (during which Extension 
Periods the Company shall have the right to make partial payments of interest 
on any Interest Payment Date, and at the end of which the Company shall pay 
all interest then accrued and unpaid (together with Additional Interest 
thereon to the extent permitted by applicable law)); provided, however, that 
no Extension Period shall extend beyond the Stated Maturity of the principal 
of this Security; provided, further, that during any such Extension Period, 
the Company shall not, and shall not permit any Subsidiary of the Company to, 
(i) declare or pay any dividends or distributions on, or redeem, purchase, 
acquire or make a liquidation payment with respect to, any of the Company's 
capital stock (which includes common and preferred stock), (ii) make any 
payment of principal of or interest or premium, if any, on or repay, 
repurchase or redeem any debt security of the Company (including Securities 
issued by the Company pursuant to the 



Indenture other than the Securities represented by this certificate) that 
ranks PARI PASSU with or junior in interest to this Security, (iii) make any 
guarantee payments with respect to any guarantee by the Company of the debt 
securities of any Subsidiaries of the Company (if such guarantee ranks PARI 
PASSU in all respects with or junior in interest to this Security) (other 
than (a) dividends or distributions in capital stock of the Company (which 
includes common and preferred stock), (b) any declaration of a dividend in 
connection with the implementation of a stockholders' rights plan, or the 
issuance of stock under any such plan in the future or the redemption or 
repurchase of any such rights pursuant thereto, (c) payments under the 
Silicon Valley Bancshares Guarantee related to the Trust Preferred Securities 
issued by SVB Capital I, and (d) purchases of Common Stock related to the 
issuance of Common Stock or rights under any of the Company's benefit plans 
for its directors, officers or employees) or (iv) redeem, purchase or acquire 
less than all of the Securities represented by this certificate or any of the 
Preferred Securities.  Prior to the termination of any such Extension Period, 
the Company may further extend such Extension Period, provided that such 
extension does not cause such Extension Period to exceed 20 consecutive 
interest payment periods or to extend beyond the Stated Maturity.  Upon the 
termination of any such Extension Period and upon the payment of all amounts 
then due on any Interest Payment Date, and subject to the foregoing 
limitation, the Company may elect to begin a new Extension Period.  No 
interest shall be due and payable during an Extension Period except at the 
end thereof.  The Company shall give the Trustee, the Property Trustee and 
the Administrative Trustees of SVB Capital I notice of its election to begin 
any Extension Period at least one Business Day prior to the earlier of (i) 
the date on which Distributions on the Trust Preferred Securities would be 
payable except for the election to begin such Extension Period, (ii) the date 
the Administrative Trustees are required to give notice to the New York Stock 
Exchange, the Nasdaq National Market or other applicable stock exchange or 
automated quotation system on which the Preferred Securities are then listed 
or quoted or to holders of such Preferred Securities of the record date, or 
(iii) the date such Distributions are payable, but in any event not less than 
one Business Day prior to such record date.  The Trustee shall give notice of 
the Company's election to begin a new Extension Period to the holders of the 
Preferred Securities.  There is no limitation on the number of times that the 
Company may elect to begin an Extension Period.

     Payment of the principal of (and premium, if any) and interest on this 
Security will be made at the office or agency of the Trustee or at the office 
of such paying agent or paying agents as the Company may designate from time 
to time, maintained for that purpose in the United States, in such coin or 
currency of the United States of America as at the time of payment is legal 
tender for payment of public and private debts; provided, however, that at 
the option of the Company payment of interest may be made (i) by check mailed 
to the address of the person entitled thereto as such address shall appear in 
the Securities Register of (ii) by transfer to an account maintained by the 
person entitled thereto, in immediately available funds, at such place and to 
such account as may be designated by the Person entitled thereto as specified 
in the Securities Register.

     The indebtedness evidenced by this Security is, to the extent provided 
in the Indenture, unsecured and will rank junior and subordinate and subject 
in right of payments to the prior payment in full of all Senior and 
Subordinated Debt, and this Security is issued subject to 



the provisions of the Indenture with respect thereto.  Each Holder of this 
Security, by accepting the same, (a) agrees to and shall be bound by such 
provisions, (b) authorizes and directs the Trustee on his behalf to take such 
actions as may be necessary or appropriate to effectuate the subordination so 
provided, and (c) appoints the Trustee his attorney-in-fact for any and all 
such purposes.  Each Holder hereof, by his acceptance hereof, waives all 
notice of the acceptance of the subordination provisions contained herein and 
in the Indenture by each holder of Senior and Subordinated Debt, whether now 
outstanding or hereafter incurred, and waives reliance by each such holder 
upon said provisions.

     Reference is hereby made to the further provisions of this Security set 
forth on the reverse hereof, which further provisions shall for all purposes 
have the same effect as if set forth at this place.

     Unless the certificate of authentication hereon has been executed by the 
Trustee referred to on the reverse hereof by manual signature, this Security 
shall not be entitled to any benefit under the Indenture or be valid or 
obligatory for any purpose.

     IN WITNESS WHEREOF, the Company has caused this instrument to be duly 
executed under its corporate seal.



                                       SILICON VALLEY BANCSHARES


                                       By:     /s/ John C. Dean
                                               ------------------------------
                                       Name:   John C. Dean
                                       Title:  President and Chief Executive 
                                               Officer


Attest:


By:     A. Catherine Ngo
    ------------------------------
Name:   A. Catherine Ngo
Title:  Executive Vice President 
        and Secretary



     This is one of the Securities referred to in the within mentioned 
Indenture.


Dated:  May 22, 1998

                                       WILMINGTON TRUST COMPANY
                                       as Trustee


                                       By:  /s/ Denise M. Geran
                                            ------------------------------
                                            Authorized Officer



                              [Reverse of Security]

     This Security is one of a duly authorized issue of securities of the 
Company (herein called the "Securities"), issued and to be issued in one or 
more series under a Junior Subordinated Indenture, dated as of May 22, 1998 
(herein called the "Indenture"), between the Company and Wilmington Trust 
Company, as Trustee (herein called the "Trustee", which term includes any 
successor trustee under the Indenture), to which Indenture and all indentures 
supplemental thereto reference is hereby made for a statement of the 
respective rights, limitations of rights, duties and immunities thereunder of 
the Trustee, the Company and the Holders of the Securities, and of the terms 
upon which the Securities are, and are to be, authenticated and delivered.  
This Security is one of the series designated on the face hereof, limited in 
aggregate principal amount to $41,237,125.

     All terms used in this Security that are defined in the Indenture and in 
the Amended and Restated Trust Agreement, dated as of May 22, 1998, as 
amended (the "Trust Agreement"), for SVB Capital I among Silicon Valley 
Bancshares, as Depositor, and the Trustees named therein, shall have the 
meanings assigned to them in the Indenture or the Trust Agreement, as the 
case may be.

     The Company may at any time, at its option, on or after June 15, 2003, 
and subject to the terms and conditions of Article XI of the Indenture, and 
subject to the Company having received any necessary regulatory approval to 
do so if then required under applicable capital guidelines or policies, 
redeem this Security in whole at any time or in part from time to time, 
without premium or penalty, at a redemption price equal to the accrued and 
unpaid interest on the Security so redeemed to the Redemption Date, plus 100% 
of the principal amount thereof.

     Upon the occurrence and during the continuation of a Tax Event, 
Investment Company Event or Capital Treatment Event, the Company may, at its 
option, at any time within 90 days of the occurrence of such Tax Event, 
Investment Company Event or Capital Treatment Event redeem this Security, in 
whole but not in part, subject to the provisions of Section 11.7 and the 
other provisions of Article XI of the Indenture, at a redemption price equal 
to the accrued and unpaid interest on the Security so redeemed to the 
Redemption Date, plus 100% of the principal amount thereof.

     In the event of redemption of this Security in part only, a new Security 
or Securities of this series for the portion hereof not redeemed will be 
issued in the name of the Holder hereof upon the cancellation hereof.

     The Indenture contains provisions for satisfaction and discharge of the 
entire indebtedness of this Security upon compliance by the Company with 
certain conditions set forth in the Indenture.

     The Indenture permits, with certain exceptions as therein provided, the 
Company and the Trustee at any time to enter into a supplemental indenture or 
indentures for the purpose 



of modifying in any manner the rights and obligations of the Company and of 
the Holders of the Securities, with the consent of the Holders of not less 
than a majority in principal amount of the Outstanding Securities of each 
series to be affected by such supplemental indenture.  The Indenture also 
contains provisions permitting Holders of specified percentages in principal 
amount of the Securities of each series at the time Outstanding, on behalf of 
the Holders of all Securities of such series, to waive compliance by the 
Company with certain provisions of the Indenture and certain past defaults 
under the Indenture and their consequences.  Any such consent or waiver by 
the Holder of this Security shall be conclusive and binding upon such Holder 
and upon all future Holders of this Security and of any Security issued upon 
the registration of transfer hereof or in exchange therefor or in lieu 
hereof, whether or not notation of such consent or waiver is made upon this 
Security.

     As provided in and subject to the provisions of the Indenture, if an 
Event of Default with respect to the Securities of this series at the time 
Outstanding occurs and is continuing, then and in every such case the Trustee 
or the Holders of not less than 25% in principal amount of the Outstanding 
Securities of this series may declare the principal amount of all the 
Securities of this series to be due and payable immediately, by a notice in 
writing to the Company (and to the Trustee if given by Holders), provided 
that, in the case of the Securities of this series issued to Cede & Co. for 
the benefit of SVB Capital I, if upon an Event of Default, the Trustee or the 
Holders of not less than 25% in principal amount of the Outstanding 
Securities of this series fails to declare the principal of all the 
Securities of this series to be immediately due and payable, the holders of 
at least 25% in aggregate Liquidation Amount of the Trust Preferred 
Securities then outstanding shall have such right by a notice in writing to 
the Company and the Trustee; and upon any such declaration the principal 
amount of and the accrued interest (including any Additional Interest) on all 
the Securities of this series shall become immediately due and payable, 
provided that the payment of principal and interest (including any Additional 
Interest) on such Securities shall remain subordinated to the extent provided 
in Article XIII of the Indenture.

     No reference herein to the Indenture and no provision of this Security 
or of the Indenture shall alter or impair the obligation of the Company, 
which is absolute and unconditional, to pay the principal of (and premium, if 
any) and interest on this Security at the times, place and rate, and in the 
coin or currency, herein prescribed.

     As provided in the Indenture and subject to certain limitations therein 
set forth, the transfer of this Security is registrable in the Securities 
Register, upon surrender of this Security for registration of transfer at the 
office or agency of the Company maintained under Section 10.2 of the 
Indenture duly endorsed by, or accompanied by a written instrument of 
transfer in form satisfactory to the Company and the Securities Registrar 
duly executed by, the Holder hereof or his attorney duly authorized in 
writing and thereupon one or more new Securities of this series, of 
authorized denominations and for the same aggregate principal amount, will be 
issued to the designated transferee or transferees.  No service charge shall 
be made for any such registration of transfer or exchange, but the Company 
may require payment of a sum sufficient to cover any tax or other 
governmental charge payable in connection therewith.



     Prior to due presentment of this Security for registration of transfer, 
the Company, the Trustee and any agent of the Company or the Trustee may 
treat the Person in whose name this Security is registered as the owner 
hereof for all purposes, whether or not this Security be overdue, and neither 
the Company, the Trustee nor any such agent shall be affected by notice to 
the contrary.

     The Securities of this series are issuable only in registered form 
without coupons in denominations of minimum denominations of $25 and any 
integral multiples of $25 in excess thereof.  As provided in the Indenture 
and subject to certain limitations therein set forth, Securities of this 
series are exchangeable for a like aggregate principal amount of Securities 
of such series of a different authorized denomination, as requested by the 
Holder surrendering the same.

     The Company and, by its acceptance of this Security or a beneficial 
interest therein, the Holder of, and any Person that acquires a beneficial 
interest in, this Security agree that for United States Federal, state and 
local tax purposes it is intended that this Security constitute indebtedness.

     THE INDENTURE AND THIS SECURITY SHALL BE GOVERNED BY AND CONSTRUED IN 
ACCORDANCE WITH THE LAWS OF THE STATE OF CALIFORNIA WITHOUT REGARD TO 
CONFLICTS OF LAWS PRINCIPLES THEREOF.