Document:

Exhibit 10.14

 Exhibit 10.14 

REGISTRATION RIGHTS AGREEMENT 

This Registration Rights Agreement (the “Agreement”) is made and entered into as of this 26th day of September 2012 by and
among Square 1 Financial, Inc., a Delaware corporation (the “Corporation”) and each of the other persons executing this Agreement (each, a “Holder” and collectively, the “Holders”), and is entered
into in connection with the Stock Purchase Agreement by and among the Corporation and the Holders dated the date hereof (the “Stock Purchase Agreement”). 

The parties hereby agree as follows: 
  

	 	1.	Certain Definitions. 

 Capitalized terms used herein which are defined in the Stock
Purchase Agreement shall have the meanings set forth in the Stock Purchase Agreement, unless otherwise defined herein. As used in this Agreement, the following terms shall have the following meanings: 

“Affiliate” means, with respect to any person, any other person which directly or indirectly controls, is controlled by, or
is under common control with, such person. 
 “Business Day” means a day, other than a Saturday or Sunday, on which banks
in New York are open for the general transaction of business. 
 “Common Stock” means the Corporation’s Class A
Common Stock, par value $0.01 per share and any securities into which such shares may hereinafter be reclassified, together with the Corporation’s Class B Non-Voting Common Stock, par value $0.01 per share and any securities into which such
shares may hereinafter be reclassified. 
 “Exchange Act” means the Securities Exchange Act of 1934, as amended, and the
rules and regulations promulgated thereunder. 
 “FINRA” means the Financial Industry Regulatory Authority, Inc. 

“Prospectus” means the prospectus included in any Registration Statement (as defined below), as amended or supplemented by
any prospectus supplement, with respect to the terms of the offering of any portion of the Registrable Securities covered by such Registration Statement and by all other amendments and supplements to the prospectus, including post-effective
amendments and all material incorporated by reference in such prospectus. 
 “Purchaser” means any person which purchases
shares of Common Stock in the Private Placement and any Affiliate or permitted transferee of any such Purchaser who is a subsequent holder of any Registrable Securities. 

“Register,” “registered” and “registration” refer to a registration made by preparing and
filing a Registration Statement or similar document in compliance with the Securities Act (as defined below), and the declaration or ordering of effectiveness of such Registration Statement or document. 

  
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 “Registrable Securities” means (i) the Shares and (ii) any shares of
Common Stock issued as, or issuable upon the conversion or exercise of any warrant, right or other security that is issued as, a dividend or other distribution with respect to, or in exchange for or in replacement of, the Shares; provided,
that, a security shall cease to be a Registrable Security upon sale pursuant to a Registration Statement or pursuant to Rule 144 under the Securities Act. 

“Registration Statement” means any registration statement of the Corporation filed under the Securities Act that covers the
resale of any of the Registrable Securities pursuant to the provisions of this Agreement (including any registration statement referred to in Section 2), amendments and supplements to such Registration Statement(s), including the Prospectus,
post-effective amendments, all exhibits and all material filed and incorporated by reference in such Registration Statement. 

“Required Purchasers” means Purchasers holding a majority of the Registrable Securities. 

“SEC” means the U.S. Securities and Exchange Commission. 

“Securities Act” means the Securities Act of 1933, as amended, and the rules and regulations promulgated thereunder. 

“Shares” means all of the shares of Common Stock held by one or more Purchasers. 

 

	 	2.	Registration. 

 (a) Registration Statement. 

(i) If the Corporation determines (by vote of the Corporation’s Board of Directors) to register any of its securities under the
Securities Act for sale to the public (except with respect to registration statements on Forms S-4, S-8 or another form not available for registering the Registrable
Securities for sale to the public) at any time after the date of this Agreement, each such time the Corporation will give written notice at the applicable address of record to the Purchasers of its intention to do so. Upon the written request of any
person then holding Registrable Securities, given within 20 days after receipt by the Purchasers of such notice, the Corporation will, subject to the limits contained in this Section 2, use its best efforts to cause all such Registrable
Securities of the requesting Holders to be registered under the Securities Act and qualified for sale under any state blue sky law, all to the extent required to permit such sale or other disposition of said Registrable Securities; provided,
however, that (A) if the Corporation is advised in writing in good faith by any managing underwriter of the Corporation’s securities being offered in a public offering pursuant to such Registration Statement that the amount to be
sold by persons other than the Corporation (collectively, “Selling Stockholders”) is greater than the amount which can be offered without adversely affecting the offering, the Corporation may reduce the amount offered for the
accounts of Selling Stockholders (including such Holders of shares of Registrable Securities) to a number deemed satisfactory by such managing underwriter; and (B) (1) in no event shall the amount of Registrable Securities of selling
Purchasers be reduced below 10% of the total amount of securities included in such offering; and (2) any shares to be excluded shall be determined in the 

  
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following order of priority: (a) securities held by any person not having any contractual, incidental registration rights, (b) securities held by any person having contractual,
incidental registration rights pursuant to an agreement which is not this Agreement, and (c) the Registrable Securities sought to be included by the Holders thereof as determined on a pro rata basis (based upon the aggregate number of
Registrable Securities held by such holders). 
 (ii) At any time after 180 days after the closing of the initial public offering of the
Common Stock pursuant to an effective registration under the Securities Act, one or more Purchasers, provided that the Purchasers collectively hold at least 10% of the Registrable Securities, may notify the Corporation that they intend to offer or
cause to be offered for public sale all or any portion of their Registrable Securities in the manner specified in such request. Such request may specify that the Corporation register Registrable Securities on a shelf registration statement (a
“Shelf Registration Statement”) on Form S-3 that contains a prospectus in such form as to permit the Purchasers to sell all such Registrable Securities at any time beginning on or after the effective date thereof pursuant to Rule
415 under the Securities Act at any time which the Corporation is eligible to use such Shelf Registration Statement, and any such Shelf Registration Statement shall in all events and notwithstanding any other provision of this Agreement register all
Registrable Securities. Upon receipt of a request for registration, the Corporation shall promptly deliver notice of such request to all Purchasers holding Registrable Securities specifying the method of registration, who shall then have 30 days to
notify the Corporation in writing of their desire to be included in such registration if such registration request does not relate to a Shelf Registration Statement. If the request for registration contemplates an underwritten public offering,
Corporation shall state such in the written notice and in such event the right of any person to participate in such registration (other than a registration on a Shelf Registration Statement) shall be conditioned upon such person’s participation
in such underwritten public offering and the inclusion of such person’s Registrable Securities in the underwritten public offering to the extent provided herein. If at any time following the filing of any Shelf Registration Statement,
Purchasers that collectively hold at least 10% of the Registrable Securities desire to sell all or any portion of the Registrable Securities under such Shelf Registration Statement pursuant to an underwritten offering (an “Underwritten
Takedown”), they will so notify the Corporation of such intention at least 15 days prior to any such sale, and the Corporation shall provide notice of such intended Underwritten Takedown to all Purchasers holding Registrable Securities
specifying the method of registration, who shall then have 10 days to notify the Corporation in writing of their desire to have their Registrable Securities included in such Underwritten Takedown. 

(iii) The Corporation will use its best efforts to expeditiously effect the registration under the Securities Act of all Registrable
Securities whose Holders request participation in such registration; provided, however, that the Corporation shall not be required to effect registration pursuant to a request under this Section 2 more than once for the Holders of
the Registrable Securities as a group if the Corporation has registered all Registrable Securities on a Shelf Registration Statement; otherwise, the Corporation shall not be required to effect registration pursuant to a request under this
Section 2 more than two times for the holders of Registrable Securities as a group. Notwithstanding anything to the contrary contained herein, no request may be made under this Section 2 within 90 days after the effective date of a
registration statement filed by the Corporation covering a firm commitment underwritten public offering in which the holders of Registrable Securities shall have been entitled to join pursuant to 

  
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Section 2(a)(iv) or demand pursuant to Section 2(a)(i) and in which there shall have been registered all Registrable Securities as to which registration shall have been requested. A
registration will not count as a requested registration under Section 2(a)(ii) unless no more than 20% of the Registrable Securities requested to be included in such Registration Statement are not included pursuant to Section 2(a)(iv)
below, and (B) unless and until the Registration Statement relating to such registration has been declared effective by the SEC at the request of the initiating shareholders; provided, however, that a majority in interest of the
participating Holders of Registrable Securities may request, in writing, that the Corporation withdraw a Registration Statement which has been filed under Section 2(a)(ii) but has not yet been declared effective, and a majority in interest of
such Holders may thereafter request the Corporation to reinstate such Registration Statement, if permitted under the Securities Act; or to file another Registration Statement, in accordance with the procedures set forth herein and without reduction
in the number of demand registrations permitted under this Section 2(a)(iii). 
 (iv) If a requested registration pursuant to
Section 2(a)(ii) involves an underwritten public offering and the managing underwriter of such offering determines in good faith that the number of securities sought to be offered should be limited due to market conditions, then the number of
securities to be included in such underwritten public offering shall be reduced to a number deemed satisfactory by such managing underwriter; provided, that the shares to be excluded shall be determined in the following order of priority:
(A) persons not having any contractual or other right to include such securities in the Registration Statement, (B) securities held by any other persons (other than the holders of Registrable Securities) having a contractual, incidental
“piggy back” right to include such securities in the Registration Statement, (C) securities to be registered by the Corporation pursuant to such Registration Statement, (D) Registrable Securities of Holders who did not make the
original request for registration and, if necessary, (E) Registrable Securities of Holders who requested such registration pursuant to Section 2(a)(ii). If there is a reduction of the number of Registrable Securities pursuant to clauses
(D) or (E), such reduction shall be made on a pro rata basis (based upon the aggregate number of Registrable Securities held by such Holders). 

(v) With respect to a request pursuant to Section 2(a)(ii) for registration which is for an underwritten public offering or for an
Underwritten Takedown, the managing underwriter shall be chosen by the holders of a majority of the Registrable Securities to be sold in such offering, subject to the consent of the Corporation which shall not be unreasonably withheld or delayed.
The Corporation may not cause any other registration of securities for sale for its own account (other than a registration effected solely to implement an employee benefit plan or a transaction to which Rule 145 of the Securities Act is applicable)
to become effective within 90 days following the effective date of any registration required pursuant to this Section 2, which is for an underwritten public offering or for an Underwritten Takedown). 

(vi) If any Registration Statement refers to any Holder by name or otherwise as the holder of any securities of the Corporation, then such
Holder shall have the right to require (a) the insertion therein of language, in form and substance reasonably satisfactory to such Holder, to the effect that the holding by such holder of such securities is not to be construed as a
recommendation by such Holder of the investment quality of the Corporation’s securities covered thereby and that such holding does not imply that such Holder will assist in meeting any future financial requirements of the Corporation, or
(b) in the event that such reference to such 

  
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Holder by name or otherwise is not required by the Securities Act or any similar Federal or state securities or “blue sky” statute and the rules and regulations thereunder then in
force, deletion of the reference to such holder. 
 (b) Form of Registration Statement. Unless otherwise provided herein, any such
Registration Statement referred to in this Agreement shall be on Form S-3, unless the Corporation is not then eligible to file a registration statement on Form S-3 under the Securities Act, in which case such Registration Statement shall be on
Form S-1. Such Registration Statement also shall cover, to the extent allowable under the Securities Act and the rules promulgated thereunder (including Rule 416 under the Securities Act), such indeterminate number of additional shares of
Common Stock resulting from stock splits, stock dividends or similar transactions with respect to the Registrable Securities. Such Registration Statement may include shares of Common Stock and other securities for the account of other holders
without the prior written consent of the Required Purchasers, provided that the inclusion of such shares of Common Stock or securities shall not have a material adverse effect on the offer and sale of the shares registered under such Registration
Statement. The Registration Statement (and each amendment or supplement thereto, and each request for acceleration of effectiveness thereof) shall be provided to the Purchasers and their counsel prior to its filing or other submission, and the
Corporation shall include therein the reasonable comments of the Purchasers or their counsel. 
 (c) Expenses. The Corporation will
pay all expenses incurred by it associated with any Registration Statement or incident to its performance or compliance with this Agreement, including filing and printing fees, the Corporation’s counsel and accounting fees and expenses, FINRA
and filing fees of any applicable national securities exchange, and costs associated with clearing the Registrable Securities for sale under applicable state securities laws, but the Corporation shall not be liable for fees and expenses incurred by
the Purchasers (including any Purchasers’ counsel fees), or any discounts, commissions, fees of underwriters, selling brokers, dealer managers or similar securities industry professionals with respect to the Registrable Securities being
offered. 
 (d) Effectiveness. 

(i) The Corporation shall use its best efforts to file each Registration Statement within 45 calendar days after the request by the Holders
hereunder if the Registration Statement relates to a public offering of shares of Common Stock, and 60 calendar days for any other Registration Statement, and to have each Registration Statement declared effective prior to the 60th calendar day following the date that such Registration Statement was initially filed with the SEC (the “Filing Date”) (or, in the event the SEC reviews and has written comments to
the Registration Statement, the 90th calendar day following the Filing Date) (the “Effectiveness Deadline”); provided, however, that if the Corporation is notified
by the SEC that the Registration Statement will not be reviewed or is no longer subject to further review and comments, the Effectiveness Deadline as to such Registration Statement shall be the 3rd Business Day following the date on which the
Corporation is so notified if such date precedes the dates otherwise required above, and the Corporation shall use its best efforts to keep each Registration Statement continuously effective under the Securities Act until the earlier of the
following (the “Effectiveness Period”): (A) such time as all of the Registrable Securities covered by such Registration Statement have been publicly sold by the Holders, (B) there

  
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otherwise ceases to be Registrable Securities, or (C) in the case of a Shelf Registration Statement, three years from the date of filing thereof; provided that if, at the expiration
of such three-year period, any Registrable Securities remain outstanding, the Company shall use its best efforts to file on the date of expiration of such three-year period a new Shelf Registration Statement. The Corporation shall notify the
Purchasers by facsimile or e-mail as promptly as practicable, and in any event, within 48 hours, after (X) the Corporation receives written comments to a Registration Statement from the SEC, (Y) the Corporation is notified by the SEC that
the Registration Statement will not be reviewed or is no longer subject to further review and comments, and (Z) a Registration Statement is declared effective. At such time as the Corporation notifies the Purchasers that a Registration
Statement is declared effective as provided in the immediately preceding sentence, the Corporation shall simultaneously provide the Purchasers with copies of any related Prospectus to be used in connection with the sale or other disposition of the
securities covered thereby. 
 (ii) For not more than 40 consecutive calendar days or for a total of not more than 75 calendar days (which
need not be consecutive days) in any 12-month period, the Corporation may delay the disclosure of material non-public information concerning the Corporation, by deferring the filing of any Registration Statement as otherwise required under this
Section 2, or suspending the use of any Prospectus included in any registration contemplated by this Section, if such disclosure at the time is not, in the good faith opinion of the Corporation, in the best interests of the Corporation (an
“Allowed Delay”); provided, that the Corporation shall promptly (a) notify the Purchasers in writing of the existence of (but in no event, without the prior written consent of a Purchaser, shall the Corporation disclose
to such Purchaser any of the facts or circumstances regarding) an Allowed Delay, (b) advise the Purchasers in writing to cease all sales under the Registration Statement until the end of the Allowed Delay, and (c) use its best efforts to
terminate an Allowed Delay as promptly as practicable. 
 (e) Certain Events. If: (i) a Registration Statement requested
pursuant to Section 2(a)(ii) is not filed with the SEC on or prior to the 30th day after the date one or more Purchasers delivered notice to the Corporation of their intent to offer or cause
to be offered for public sale all or any portion of their Registrable Securities, or (ii) a Registration Statement that has been filed with the SEC as contemplated under Section 2(a)(i) or Section 2(a)(ii) is not declared effective by
the SEC (or otherwise does not become effective) for any reason on or prior to the Effectiveness Deadline, or (iii) after its effective date, (A) such Registration Statement ceases for any reason (including without limitation by reason of
a stop order, or the Corporation’s failure to update the Registration Statement), to remain continuously effective as to all Registrable Securities included in such Registration Statement or (B) the Holders are not permitted to utilize the
Prospectus therein to resell such Registrable Securities (x) pursuant to Section 3(a)(xiii) or (y) because of an Allowed Delay and the 40 consecutive calendar- or 75 calendar-day periods set forth in Section 2(d)(ii) above have
been exceeded, or (iv) the Corporation fails to satisfy the current public information requirement pursuant to Rule 144(c) as a result of which the Holders are unable to sell Registrable Securities without restriction (other than volume
limitations, manner of sale restrictions and notice filing requirements that may apply if the Holder is an “affiliate” of the Corporation, as that term is defined in Rule 144(a)(1)) under Rule 144 (or any successor thereto), (any such
failure or breach in clauses (i) through (iv) above being referred to as an “Event,” and, for purposes of clauses (i), (ii) or (iv), the date on which such Event occurs, or for purposes of clause (iii), the date on
which such 40 consecutive 

  
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calendar-day or 75 calendar-day period is exceeded, being referred to as an “Event Date”), then in addition to any other rights the Holders may have hereunder or under applicable
law, on each such Event Date and on each monthly anniversary of each such Event Date (if the applicable Event shall not have been cured by such date) until the earlier of (1) the applicable Event is cured or (2) the Registrable Securities
are eligible for resale pursuant to Rule 144 without manner of sale or volume restrictions, the Corporation shall pay to each Holder an amount in cash, as partial liquidated damages and not as a penalty (“Liquidated Damages”), equal
to 1.0% of the aggregate purchase price paid by such Holder pursuant to the Stock Purchase Agreement for any unregistered Registrable Securities held by such Holder on the Event Date. The parties agree that notwithstanding anything to the contrary
herein or in the Stock Purchase Agreement, no Liquidated Damages shall be payable with respect to any period after the expiration of the Effectiveness Period (except in respect of an Event described in Section 2(e)(iv) herein) (it being
understood that this sentence shall not relieve the Corporation of any Liquidated Damages accruing prior to the Effectiveness Deadline) and in no event shall the aggregate amount of Liquidated Damages (excluding Liquidated Damages payable in respect
of an Event described in Section 2(e)(iv) herein) payable to a Holder exceed, in the aggregate, 6% of the aggregate purchase price paid by such Holder pursuant to the Stock Purchase Agreement (12% in respect of an Event described in
Section 2(e)(iv) herein). If the Corporation fails to pay any Liquidated Damages pursuant to this Section in full within 5 Business Days after the date payable, the Corporation will pay interest thereon at a rate of 1.0% per month (or such
lesser maximum amount that is permitted to be paid by applicable law) to the Holder, accruing daily from the date such Liquidated Damages are due until such amounts, plus all such interest thereon, are paid in full. The Liquidated Damages pursuant
to the terms hereof shall apply on a daily pro-rata basis for any portion of a month prior to the cure of an Event, except in the case of the first Event Date. 
  

	 	3.	Corporation Obligations. 

 (a) The Corporation will use its best efforts to effect the
registration of the Registrable Securities in accordance with the terms hereof, and pursuant thereto the Corporation will (but subject to Section 2(d)(ii)): 

(i) (A) promptly furnish to the Purchasers, copies of all such documents proposed to be filed, which documents will be subject to the review
of such Purchasers, and (B) cause its officers and directors, counsel and independent certified public accountants to respond to such inquiries as shall be necessary, to conduct a reasonable review of such documents. The Corporation shall not
file the Registration Statement or any such Prospectus of any amendments or supplements thereto to which the holders of a majority of the Registrable Securities shall object in writing within 3 Business Days of their receipt thereof if:
(1) such objection relates specifically to any description in the Registration Statement, Prospectus or amendment or supplement thereto of the Purchasers, any Affiliate of any Purchaser (other than the Corporation if the Corporation is an
Affiliate of any Purchaser) or the Shares, or (2) the Shares, the resale of which is covered by the Registration Statement, Prospectus, amendment or supplement, represent more than 50% of all shares of Common Stock, the sale and/or resales of
which are covered by such Registration Statement, Prospectus, amendment or supplement. 

  
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 (ii) respond promptly to any comments received from the SEC with respect to the Registration
Statement or any amendment thereto and as promptly as possible provide the Purchasers true and complete copies of all correspondence from and to the SEC relating to the Registration Statement. 

(iii) notify the Purchasers promptly (and, in the case of (A)(1) below, not less than 3 days prior to such filing) and (if requested by any
such Person) confirm such notice in writing no later than 2 Business Days following the day (A)(1) when a Prospectus or any Prospectus supplement or post-effective amendment to the Registration Statement is filed; (2) when the SEC notifies the
Corporation whether there will be a “review” of such Registration Statement and whenever the SEC provides comments in writing or orally on such Registration Statement and (3) with respect to the Registration Statement or any
post-effective amendment, when the same has become effective; (B) of any request by the SEC or any other Federal or state governmental authority for amendments or supplements to the Registration Statement or Prospectus or for additional
information; (C) of the issuance by the SEC of any stop order suspending the effectiveness of the Registration Statement covering any or all of the Registrable Securities or the initiation or threatening of any Proceedings for that purpose;
(D) if at any time any of the representations and warranties of the Corporation contained in any agreement contemplated hereby cease to be true and correct in all material respects; (E) of the receipt by the Corporation of any notification
with respect to the suspension of the qualification or exemption from qualification of any of the Registrable Securities for sale in any jurisdiction, or the initiation of any Proceeding for such purpose; and (F) of the occurrence of any event
that makes any statement made in the Registration Statement or Prospectus or any document incorporated or deemed to be incorporated therein by reference untrue in any material respect or that requires any revisions to the Registration Statement,
Prospectus or other documents so that, in the case of the Registration Statement or the Prospectus, as the case may be, it will not contain any untrue statement of a material fact or omit to state any material fact required to be stated therein or
necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading. 
 (iv) if
requested by the Required Purchasers, (i) promptly incorporate in a Prospectus supplement or post-effective amendment to the Registration Statement such information as the Corporation reasonably agrees should be included therein and
(ii) make all required filings of such Prospectus supplement or such post-effective amendment as soon as practicable after the Corporation has received notification of the matters to be incorporated in such Prospectus supplement or
post-effective amendment. 
 (v) promptly deliver to each Purchaser, without charge, as many copies of the Prospectus or Prospectuses
(including each form of prospectus) and each amendment or supplement thereto as such Persons may reasonably request. 
 (vi) (i) furnish to
each Purchaser a signed counterpart, addressed to the Purchaser, of an opinion of counsel for the Corporation, dated the effective date of the Registration Statement, and (ii) subject only to the obligation of the Corporation to use its best
efforts, furnish to each Purchaser a “comfort” letter signed by the independent public accountants who have certified the Corporation’s financial statements included in the Registration Statement, covering substantially the same
matters with respect to the Registration Statement (and the 

  
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prospectus included therein) and (in the case of the accountants’ letter) with respect to events subsequent to the date of the financial statements, as are customarily covered (at the time
of such registration) in opinions of the Corporation’s counsel and in accountants’ letters delivered to the underwriters in underwritten public offerings of securities; 

(vii) cooperate with the Purchasers to facilitate the timely preparation and delivery of certificates representing Registrable Securities to
be sold pursuant to a Registration Statement, which certificates, to the extent permitted by applicable federal and state securities laws, shall be free of all restrictive legends, and to enable such Registrable Securities to be in such
denominations and registered in such names as any Purchaser may request in connection with any sale of Registrable Securities; 
 (viii)
prepare and file with the SEC such amendments and post-effective amendments to the Registration Statement and the Prospectus as may be necessary to keep the Registration Statement effective for the Effectiveness Period and to comply with the
provisions of the Securities Act and the Exchange Act with respect to the distribution of all of the Registrable Securities covered thereby in accordance with the intended method of disposition as set forth in the Registration Statement, Prospectus
or Prospectus supplement; 
 (ix) correct any deficiency (in the judgment of either the Corporation or the Holders) between the preliminary
prospectus and the final prospectus, and pay any expenses associated with the recirculation of the final prospectus following the correction of such deficiency; 

(x) use its best efforts to (i) prevent the issuance of any stop order or other suspension of effectiveness or qualification or
exemption of qualification and, (ii) if such order is issued, obtain the prompt withdrawal of any such order; 
 (xi) prior to any
public offering of Registrable Securities, use reasonable best efforts to register or qualify or cooperate with the Purchasers and their counsel in connection with the registration or qualification of such Registrable Securities for offer and sale
under the securities or blue sky laws of such jurisdictions requested by the Purchasers, to keep such registration or qualification effective during the Effectiveness Period and do any and all other acts or things necessary or advisable to enable
the distribution in such jurisdictions of the Registrable Securities covered by the Registration Statement; provided, however, that the Corporation shall not be required in connection therewith or as a condition thereto to
(i) qualify to do business in any jurisdiction where it would not otherwise be required to qualify but for this Section 3, (ii) subject itself to general taxation in any jurisdiction where it would not otherwise be so subject but for
this Section 3, or (iii) file a general consent to service of process in any such jurisdiction; 
 (xii) use its best efforts to
cause all Registrable Securities covered by a Registration Statement to be listed on each securities exchange, interdealer quotation system or other market on which similar securities issued by the Corporation are then listed; 

(xiii) promptly notify the Purchasers, at any time when a Prospectus relating to Registrable Securities is required to be delivered under the
Securities Act (including 

  
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during any period when the Corporation is in compliance with Rule 172), upon discovery that, or upon the happening of any event as a result of which, the Registration Statement (including the
Prospectus), as then in effect, includes an untrue statement of a material fact or omits to state any material fact required to be stated therein or necessary to make the statements therein not misleading in light of the circumstances then existing,
and at the request of any such holder, promptly prepare, file with the SEC pursuant to Rule 172 and furnish to such holder a supplement to or an amendment of such Prospectus or post-effective amendment to such Registration Statement (and have it
declared effective as promptly as practicable) as may be necessary so that such Prospectus shall not include an untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements
therein not misleading in light of the circumstances then existing; 
 (xiv) otherwise use its best efforts to comply with all applicable
rules and regulations of the SEC under the Securities Act and the Exchange Act, including Rule 172, notify the Purchasers promptly if the Corporation no longer satisfies the conditions of Rule 172 and take such other actions as may be reasonably
necessary to facilitate the registration of the Registrable Securities hereunder; and make available to its security holders, as soon as reasonably practicable, but not later than the Availability Date (as defined below), an earning statement
covering a period of at least 12 months, beginning after the effective date of each Registration Statement, which earning statement shall satisfy the provisions of Section 11(a) of the Securities Act, including Rule 158 promulgated thereunder
(for the purpose of this Section 3, “Availability Date” means the 45th day following the end of the fourth fiscal quarter that includes the effective date of such Registration Statement, except that, if such fourth fiscal quarter is
the last quarter of the Corporation’s fiscal year, “Availability Date” means the 90th day after the end of such fourth fiscal quarter); 

(xv) upon written notice from a Purchaser that such Purchaser has a legal obligation to make a filing with the FINRA Corporate Financing
Department pursuant to FINRA Rule 5110 with respect to the public offering contemplated by the Registration Statement (an “Issuer Filing”), the Corporation agrees it will effect such filing prior to the later to occur of five
Trading Days after receipt of the written notice and one Trading Day after the date that the Registration Statement is first filed with the SEC. The Corporation shall use reasonable best efforts to pursue the Issuer Filing until the FINRA issues a
letter confirming that it does not object to the terms of the offering contemplated by the Registration Statement. The Corporation will pay any filing fees and expenses in connection with the Issuer Filing; 

(xvi) in any underwritten offering, including any Underwritten Take-Down Transaction: 

(A) If requested by the underwriters, the Corporation shall enter into an underwriting agreement with the underwriters for such offering, such
agreement to be reasonably satisfactory in substance and form to the underwriters and the Holders of Registrable Securities participating in such underwritten offering; and 

(B) cause its officers and employees to participate in, and to otherwise facilitate and cooperate with the preparation of the Registration
Statement and prospectus and any amendments or supplements thereto (including participating in meetings, drafting sessions 

  
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and due diligence sessions) and to prepare for, and participate in “road shows,” and all such other customary selling efforts as the Holders of a majority of the Registrable Securities
participating in such offering or the underwriters reasonably request in order to expedite or facilitate such disposition but in each case taking into account the Corporation’s business needs; provided that, notwithstanding anything to
the contrary herein, the total number of “road shows” the Corporation shall be required to participate in pursuant to this Agreement shall not exceed two in each case; 

(b) With a view to making available to the Purchasers the benefits of Rule 144 (or its successor rule) and any other rule or regulation of the
SEC that may at any time permit the Purchasers to sell shares of Common Stock to the public without registration, the Corporation covenants and agrees to: make and keep public information available, as those terms are understood and defined in Rule
144, until such date as all of the Registrable Securities shall have been resold; (ii) file with the SEC in a timely manner all reports and other documents required of the Corporation under the Exchange Act; and (iii) furnish to each
Purchaser upon request, as long as such Purchaser owns any Registrable Securities, (A) a written statement by the Corporation that it has complied with the reporting requirements of the Exchange Act, and (B) such other information as may
be reasonably requested in order to avail such Purchaser of any rule or regulation of the SEC that permits the selling of any such Registrable Securities without registration. 

(c) With a view to satisfying its obligations under Section 2(a), the Corporation, after the first public offering of its securities
registered under the Securities Act, shall use its best efforts to qualify and remain qualified to register securities pursuant to a registration statement and Form S-3 under the Securities Act. 

 

	 	4.	Due Diligence Review; Information. 

 (a) Subject to paragraph (b) of this
Section 4, upon reasonable prior notice, the Corporation shall make available, during normal business hours, for inspection and review by the Purchasers, advisors to and representatives of the Purchasers (who may or may not be affiliated with
the Purchasers and who are reasonably acceptable to the Corporation), and to the underwriters for any underwritten offering chosen pursuant to Section 2(a)(v), all financial and other records, all filings with the SEC, and all other corporate
documents and properties of the Corporation as may be reasonably necessary for the purpose of such review, and cause the Corporation’s officers, directors, employees and independent accountants, within a reasonable time period, to supply all
such information reasonably requested by the Purchasers or any such representative, advisor or underwriter in connection with such Registration Statement (including, without limitation, in response to all questions and other inquiries reasonably
made or submitted by any of them), prior to and from time to time after the filing and effectiveness of the Registration Statement for the sole purpose of enabling the Purchasers and such representatives, advisors and underwriters and their
respective accountants and attorneys to conduct initial and ongoing due diligence with respect to the Corporation and the accuracy of such Registration Statement. 

(b) Beginning with the filing of the Registration Statement in connection with the Corporation’s initial public offering of Common Stock
or, if earlier, the date when the 

  
 11 

 
Corporation first becomes subject to the reporting provisions under the Exchange Act applicable to issuers of securities, the Corporation shall not disclose material nonpublic information to the
Purchasers, or to advisors to or representatives of the Purchasers, unless prior to disclosure of such information the Corporation identifies such information as being material nonpublic information and provides the Purchasers, such advisors and
representatives with the opportunity to accept or refuse to accept such material nonpublic information for review and any Purchaser wishing to obtain such information enters into an appropriate confidentiality agreement with the Corporation with
respect thereto. 
  

	 	5.	Obligations of the Purchasers. 

 (a) Each Purchaser shall promptly furnish in writing to
the Corporation such information regarding itself, the Registrable Securities held by it and the intended method of disposition of the Registrable Securities held by it, as shall be reasonably required to effect the registration of such Registrable
Securities and shall execute such documents in connection with such registration as the Corporation may reasonably request. At least 10 Business Days prior to the first anticipated filing date of the Registration Statement, the Corporation shall
notify each Purchaser of the information the Corporation requires from such Purchaser if such Purchaser elects to have any of the Registrable Securities included in the Registration Statement. A Purchaser shall provide such information to the
Corporation at least 3 Business Days prior to the first anticipated filing date of such Registration Statement if such Purchaser elects to have any of the Registrable Securities included in the Registration Statement. 

(b) Each Purchaser, by its acceptance of the Registrable Securities, agrees to cooperate with the Corporation as reasonably requested by the
Corporation in connection with the preparation and filing of a Registration Statement hereunder, unless such Purchaser has notified the Corporation in writing of its election to exclude all of its Registrable Securities from such Registration
Statement. 
 (c) Each Purchaser agrees that, upon receipt of any notice from the Corporation of either (i) the commencement of an
Allowed Delay pursuant to Section 2(d)(ii) or (ii) the happening of an event pursuant to Section 3(a)(xiii) hereof, such Purchaser will immediately discontinue disposition of Registrable Securities pursuant to the Registration
Statement covering such Registrable Securities until the Purchaser is advised by the Corporation that a supplemented or amended prospectus has been filed with the SEC and until any related post-effective amendment is declared effective and, if so
directed by the Corporation, the Purchaser shall deliver to the Corporation or destroy (and deliver to the Corporation a certificate of destruction) all copies in the Purchaser’s possession of the Prospectus covering the Registrable Securities
current at the time of receipt of such notice. 
  

	 	6.	Indemnification. 

 (a) Indemnification by the Corporation. The Corporation will
indemnify and hold harmless each Purchaser and its officers, directors, members, partners, employees, attorneys and agents, successors and assigns, and each other person, if any, who controls such Purchaser within the meaning of the Securities Act
or Section 20 of the Exchange Act (and its officers, directors, partners, members and employees), against any losses, claims, damages, expenses, 

  
 12 

 
costs (including reasonable attorney fees) or liabilities, joint or several, to which they may become subject under the Securities Act or otherwise, insofar as such losses, claims, damages,
expenses, costs or liabilities (or actions in respect thereof) arise out of or are based upon: (i) any untrue statement or alleged untrue statement of any material fact contained in the Registration Statement, any preliminary prospectus or
final prospectus contained therein, or form of prospectus or any amendment or supplement thereof; (ii) the omission or alleged omission to state in the Registration Statement, any preliminary prospectus or final prospectus contained therein, or
form of prospectus or any amendment or supplement thereof, a material fact required to be stated therein or necessary to make the statements therein not misleading; (iii) any violation or alleged violation by the Corporation or its agents of
the Securities Act or any state securities law, or any rule or regulation thereunder in connection with such registration; or (iv) any failure to register or qualify the Registrable Securities included in any such Registration in any state
where the Corporation or its agents has affirmatively undertaken or agreed in writing that the Corporation will undertake such registration or qualification on a Purchaser’s behalf, and will reimburse such Purchaser, and each such officer,
director or member and each such controlling person for any legal or other expenses reasonably incurred by them in connection with investigating or defending any such loss, claim, damage, liability or action; provided, however, that
the Corporation will not be liable in any such case if and to the extent that any such loss, claim, damage or liability arises out of or is based upon an untrue statement or alleged untrue statement or omission or alleged omission so made in
conformity with information furnished by such Purchaser or any such controlling person in writing specifically for use in such Registration Statement or Prospectus. 

(b) Indemnification by the Purchasers. Each Purchaser agrees, severally but not jointly, to indemnify and hold harmless, to the fullest
extent permitted by law, the Corporation, its directors, officers, employees, stockholders and each person who controls the Corporation (within the meaning of the Securities Act) against any losses, claims, damages, liabilities and reasonable
expense (including reasonable attorney fees) resulting from any untrue statement of a material fact contained in the Registration Statement, any preliminary prospectus or final prospectus contained therein, or form of prospectus or any amendment or
supplement thereof or any omission of a material fact required to be stated in the Registration Statement, any preliminary prospectus or final prospectus contained therein, or form of prospectus or any amendment or supplement thereof or necessary to
make the statements therein, in light of the circumstances under which they were made, not misleading, to the extent, but only to the extent that such untrue statement is, and such omission is not, contained in any information furnished in writing
by such Purchaser to the Corporation specifically for inclusion in such Registration Statement or Prospectus. The liability of any Purchaser for indemnification under this Section 6(b) in its capacity as a seller of Registrable Securities shall
not exceed the lesser of (i) that proportion of the total of such losses, claims, damages, expenses or liabilities indemnified against equal to the proportion of the total securities sold under such Registration Statement held by such
Purchaser, and (ii) the amount equal to the net proceeds to such Purchaser of the securities sold in any such registration; provided that no Holder shall be required to indemnify any person against any liability arising from any untrue
or misleading statement or omission contained in any preliminary prospectus if such deficiency is corrected in the final prospectus or for any liability which arises out of the failure of any person to deliver a prospectus as required by the
Securities Act. 

  
 13 

 (c) Conduct of Indemnification Proceedings. Any person entitled to indemnification
hereunder shall (i) give prompt notice to the indemnifying party of any claim with respect to which it seeks indemnification and (ii) permit such indemnifying party to assume the defense of such claim with counsel reasonably satisfactory
to the indemnified party; provided that any person entitled to indemnification hereunder shall have the right to employ separate counsel and to participate in the defense of such claim, but the fees and expenses of such counsel shall be at
the expense of such person unless (A) the indemnifying party has agreed to pay such fees or expenses, or (B) the indemnifying party shall have failed to assume the defense of such claim and employ counsel reasonably satisfactory to such
person or (C) in the reasonable judgment of any such person, based upon written advice of its counsel, a conflict of interest exists between such person and the indemnifying party with respect to such claims (in which case, if the person
notifies the indemnifying party in writing that such person elects to employ separate counsel at the expense of the indemnifying party, the indemnifying party shall not have the right to assume the defense of such claim on behalf of such person);
and provided, further, that the failure of any indemnified party to give notice as provided herein shall not relieve the indemnifying party of its obligations hereunder, except to the extent that such failure to give notice shall
materially adversely affect the indemnifying party in the defense of any such claim or litigation. It is understood that the indemnifying party shall not, in connection with any proceeding in the same jurisdiction, be liable for fees or expenses of
more than one separate firm of attorneys at any time for all such indemnified parties. No indemnifying party will, except with the consent of the indemnified party, consent to entry of any judgment or enter into any settlement that does not include
as an unconditional term thereof the giving by the claimant or plaintiff to such indemnified party of a release from all liability in respect of such claim or litigation, does not impose any injunction or similar restriction on such indemnified
party and does not include a statement as to or an admission of fault, liability, culpability or failure to act with respect to any law by an indemnified party. 

(d) Contribution. If for any reason the indemnification provided for in the preceding paragraphs (a) and (b) of this
Section 6 is unavailable to an indemnified party or insufficient to hold it harmless, other than as expressly specified therein, then the indemnifying party shall contribute to the amount paid or payable by the indemnified party as a result of
such loss, claim, damage or liability in such proportion as is appropriate to reflect the relative fault of the indemnified party and the indemnifying party, as well as any other relevant equitable considerations. The relative fault of such
indemnifying party and indemnified party shall be determined by reference to, among other things, whether any action in question, including any untrue or alleged untrue statement of a material fact or omission or alleged omission of a material fact,
has been taken or made by, or relates to information supplied by, such indemnifying party or indemnified party, and the parties’ relative intent, knowledge, access to information and opportunity to correct or prevent such action, statement or
omission. The parties hereto agree that it would not be just and equitable if contribution pursuant to this section were determined by pro rata allocation or by any other method of allocation that does not take into account the foregoing equitable
considerations. Notwithstanding the forgoing, a holder of Registrable Securities shall not be required to contribute under this Section 6(d) in excess of the lesser of (i) that proportion of the total liability indemnified against equal to
the proportion of the total Registrable Securities sold under such Registration Statement by such holder and (ii) the net proceeds received by such holder from its sale of Registrable Securities under such Registration

  
 14 

 
Statement. No Person found guilty of fraudulent representation (within the meaning of Section 11(f) of the Securities Act) shall be entitled to contribution from any person not found guilty
of such fraudulent misrepresentation. 
  

	 	7.	Miscellaneous. 

 (a) Market Stand-Off. 

(i) Each Holder shall, if so requested by the Corporation and an underwriter of Registrable Securities in connection with any public offering
of shares of Common Stock, not directly or indirectly offer, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant for the sale of or otherwise dispose of or
transfer any shares held by it for such period, not to exceed (A) 180 days following the effective date of the relevant registration statement filed under the Securities Act in connection with the Corporation’s initial public offering of
Common Stock, or (B) 90 days following the effective date of the relevant registration statement in connection with any other public offering of Common Stock, as such underwriter shall specify reasonably and in good faith, provided,
however, that (1) all officers and directors of the Corporation and all holders of more than 5% of the outstanding shares of Common Stock (determined on a fully diluted basis) enter into agreements with terms that include provisions
substantially similar to, and each such agreement is in total consistent with, this Section 7(a)(i), (2) the Corporation uses reasonable efforts to have all holders of 25,000 or more of the outstanding shares of Common Stock (determined on
a fully diluted basis) enter into agreements with terms that include provisions similar to, and each such agreement is in total consistent with, this Section 7(a)(i), (3) if at any time the Corporation grants any of its officers or
directors a waiver of any term of any such agreement, the Corporation shall at such time grant a waiver of similar terms applicable to all other holders of Common Stock who have entered into agreements with terms that include provisions similar to
this Section 7(a)(i), including the Purchasers, with all such waivers to apply to the affected Common Stock on a pro rata basis (based upon the aggregate number of Registrable Securities held by such Holders), and (4) the limitations
applicable to each Holder in this Section 7(a)(i) only shall apply to those equity interests in the Corporation held by such Holder immediately prior to the public offering. 

(ii) The Corporation shall not effect any public sale or distribution of its equity securities, or any securities convertible into or
exchangeable or exercisable for such securities, during the seven days prior to and during the 180-day period beginning on the effective date of any registration (except as part of such underwritten registration or pursuant to registrations on Form
S-4 or S-8 or any successor form). 
 (b) Registration and Reports Under the Exchange Act. In the event that the Corporation
(i) registers a class of securities under Section 12 of the Exchange Act or (ii) shall commence to file reports under Section 13 or 15(d) of the Exchange Act, the Corporation will use its best efforts thereafter to file with the
SEC such information as is required under the Exchange Act for so long as there are holders of Registrable Securities; and in such event, the Corporation shall use its best efforts to take all action as may be required as a condition to the
availability of Rule 144 under the Securities Act (or any comparable successor rules). The Corporation shall furnish to any holder of Registrable Securities upon request a written statement 

  
 15 

 
executed by the Corporation as to the steps it has taken to comply with the current public information requirement of Rule 144 (or such comparable successor rules). After the occurrence of the
first underwritten public offering of Common Stock of the Corporation pursuant to an offering registered under the Securities Act on Form S-1 (or any comparable successor forms), subject to the limitations on
transfers imposed by this Agreement, the Corporation shall use its best efforts to facilitate and expedite transfers of Registrable Securities pursuant to Rule 144 under the Securities Act, which efforts shall include timely notice to its transfer
agent to expedite such transfers of Registrable Securities. 
 (c) Amendments and Waivers. This Agreement may be amended, modified or
waived only by a writing signed by the Corporation and the Required Purchasers. 
 (d) Notices. All notices and other communications
provided for or permitted hereunder shall be made as set forth in Section 7.3 of the Stock Purchase Agreement. 
 (e) Assignments
and Transfers by Purchasers. The provisions of this Agreement shall be binding upon and inure to the benefit of the Purchasers and their respective successors and assigns. A Purchaser may transfer or assign, in whole or from time to time in
part, to one or more persons its rights hereunder in connection with the transfer of Registrable Securities by such Purchaser to such person, provided that (i) (A) such person is an Affiliate of such Purchaser or
(B) immediately upon completion of any such transfer, the transferee holds at least 5% of the Registrable Securities, (ii) such Purchaser complies with all laws applicable thereto and provides written notice of assignment to the
Corporation promptly after such assignment is effected and (iii) the transferee agrees in writing to be bound by this Agreement as if it were a party hereto. 

(f) Assignments and Transfers by the Corporation. 

(i) This Agreement may not be assigned by the Corporation (whether by operation of law or otherwise) without the prior written consent of the
Required Purchasers, provided, however, that the Corporation may assign its rights and delegate its duties hereunder to any surviving or successor corporation in connection with a merger or consolidation of the Corporation with another
corporation, or a sale, transfer or other disposition of all or substantially all of the Corporation’s assets to another corporation, without the prior written consent of the Required Purchasers, after notice duly given by the Corporation to
each Purchaser. 
 (ii) Other than transferees of Registrable Securities under Section 7(e)(i), the Corporation shall not, without the
prior written consent of holders of at least a 80% of the Registrable Securities, allow purchasers of the Corporation’s securities to become a party to this Agreement. 

(g) Benefits of the Agreement. The terms and conditions of this Agreement shall inure to the benefit of and be binding upon the
respective permitted successors and assigns of the parties. Nothing in this Agreement, express or implied, is intended to confer upon any party other than the parties hereto or their respective successors and assigns any rights, remedies,
obligations, or liabilities under or by reason of this Agreement, except as expressly provided in this Agreement. 

  
 16 

 (h) Counterparts; Faxes. This Agreement may be executed in two or more counterparts, each
of which shall be deemed an original, but all of which together shall constitute one and the same instrument. This Agreement may also be executed via facsimile, which shall be deemed an original. 

(i) Titles and Subtitles. The titles and subtitles used in this Agreement are used for convenience only and are not to be considered in
construing or interpreting this Agreement. 
 (j) Severability. Any provision of this Agreement that is prohibited or unenforceable
in any jurisdiction shall, as to such jurisdiction, be ineffective to the extent of such prohibition or unenforceability without invalidating the remaining provisions hereof but shall be interpreted as if it were written so as to be enforceable to
the maximum extent permitted by applicable law, and any such prohibition or unenforceability in any jurisdiction shall not invalidate or render unenforceable such provision in any other jurisdiction. To the extent permitted by applicable law, the
parties hereby waive any provision of law which renders any provisions hereof prohibited or unenforceable in any respect. 
 (k) Further
Assurances. The parties shall execute and deliver all such further instruments and documents and take all such other actions as may reasonably be required to carry out the transactions contemplated hereby and to evidence the fulfillment of the
agreements herein contained. 
 (l) Entire Agreement. This Agreement is intended by the parties as a final expression of their
agreement and intended to be a complete and exclusive statement of the agreement and understanding of the parties hereto in respect of the subject matter contained herein. This Agreement supersedes all prior agreements and understandings between the
parties with respect to such subject matter. 
 (m) Governing Law; Consent to Jurisdiction; Waiver of Jury Trial. This Agreement
shall be governed by, and construed in accordance with, the internal laws of the State of Delaware without regard to the choice of law principles thereof. Each of the parties hereto irrevocably submits to the exclusive jurisdiction of the courts of
the State of Delaware for the purpose of any suit, action, proceeding or judgment relating to or arising out of this Agreement and the transactions contemplated hereby. Service of process in connection with any such suit, action or proceeding may be
served on each party hereto anywhere in the world by the same methods as are specified for the giving of notices under this Agreement. Each of the parties hereto irrevocably consents to the jurisdiction of any such court in any such suit, action or
proceeding and to the laying of venue in such court. Each party hereto irrevocably waives any objection to the laying of venue of any such suit, action or proceeding brought in such courts and irrevocably waives any claim that any such suit, action
or proceeding brought in any such court has been brought in an inconvenient forum. EACH OF THE PARTIES HERETO WAIVES ANY RIGHT TO REQUEST A TRIAL BY JURY IN ANY LITIGATION WITH RESPECT TO THIS AGREEMENT AND REPRESENTS THAT COUNSEL HAS BEEN
CONSULTED SPECIFICALLY AS TO THIS WAIVER. 

  
 17 

 (n) Obligations of Purchasers. The Corporation acknowledges that the obligations of each
Purchaser under this Agreement are several and not joint with the obligations of any other Purchaser, and no Purchaser shall be responsible in any way for the performance of the obligations of any other Purchaser under this Agreement. The decision
of each Purchaser to enter into to this Agreement has been made by such Purchaser independently of any other Purchaser. The Corporation further acknowledges that nothing contained in this Agreement, and no action taken by any Purchaser pursuant
hereto, shall be deemed to constitute the Purchasers as a partnership, an association, a joint venture or any other kind of entity, or create a presumption that the Purchasers are in any way acting in concert or as a group with respect to such
obligations or the transactions contemplated hereby. Each Purchaser shall be entitled to independently protect and enforce its rights, including without limitation, the rights arising out of this Agreement, and it shall not be necessary for any
other Purchaser to be joined as an additional party in any proceeding for such purpose. 
 Each Purchaser has been represented by its own
separate legal counsel in their review and negotiation of this Agreement and with respect to the transactions contemplated hereby. 

[Signature pages follow] 

  
 18 

 IN WITNESS WHEREOF, the parties have executed this Agreement or caused their duly authorized
officers to execute this Agreement as of the date first written above. 
  

							
	The Corporation:	 	SQUARE 1 FINANCIAL, INC.
			
		 	By:	 	 /s/ Douglas H. Bowers

		 		 	Name:	 	Douglas Bowers
		 		 	Title:	 	President and Chief Executive Officer
		
	Purchaser:	 	 Basswood Capital Management, L.L.C.

as investment manager, on behalf of
 Basswood Financial Enhanced
Fund, L.P.

			
		 	By:	 	 /s/ Matthew Lindenbaum

		 		 	Name:	 	Matthew Lindenbaum
		 		 	Title: Principal, Basswood Capital
		 		 	Management, L.L.C.

 IN WITNESS WHEREOF, the parties have executed this Agreement or caused their duly authorized
officers to execute this Agreement as of the date first written above. 
  

							
	The Corporation:	 	SQUARE 1 FINANCIAL, INC.
			
		 	By:	 	 /s/ Douglas H. Bowers

		 		 	Name:	 	Douglas Bowers
		 		 	Title:	 	President and Chief Executive Officer
		
	Purchaser:	 	 Basswood Capital Management, L.L.C.

as investment manager, on behalf of
 Basswood Financial Fund,
L.P.

			
		 	By:	 	 /s/ Matthew Lindenbaum

		 		 	Name:	 	Matthew Lindenbaum
		 		 	Title: Principal, Basswood Capital
		 		 	Management, L.L.C.

 IN WITNESS WHEREOF, the parties have executed this Agreement or caused their duly authorized
officers to execute this Agreement as of the date first written above. 
  

							
	The Corporation:	 	SQUARE 1 FINANCIAL, INC.
			
		 	By:	 	 /s/ Douglas H. Bowers

		 		 	Name:	 	Douglas Bowers
		 		 	Title:	 	President and Chief Executive Officer
		
	Purchaser:	 	 Basswood Capital Management, L.L.C.

as investment manager, on behalf of
 Basswood Opportunity Fund,
Inc.

			
		 	By:	 	 /s/ Matthew Lindenbaum

		 		 	Name:	 	Matthew Lindenbaum
		 		 	Title: Principal, Basswood Capital
		 		 	Management, L.L.C.

 If IN WITNESS WHEREOF, the parties have executed this Agreement or caused their duly authorized
officers to execute this Agreement as of the date first written above. 
  

							
	The Corporation:	 	SQUARE 1 FINANCIAL, INC.
			
		 	By:	 	 /s/ Douglas H. Bowers

		 		 	Name:	 	Douglas Bowers
		 		 	Title:	 	President and Chief Executive Officer
		
	Purchaser:	 	 Basswood Capital Management, L.L.C.

as investment manager, on behalf of
 Basswood Opportunity
Partners, L.P.

			
		 	By:	 	 /s/ Matthew Lindenbaum

		 		 	Name:	 	Matthew Lindenbaum
		 		 	Title: Principal, Basswood Capital
		 		 	Management, L.L.C.

 IN WITNESS WHEREOF, the parties have executed this Agreement or caused their duly authorized
officers to execute this Agreement as of the date first written above. 
  

							
	The Corporation:	 	SQUARE 1 FINANCIAL, INC.
			
		 	By:	 	 /s/ Douglas H. Bowers

		 		 	Name:	 	Douglas Bowers
		 		 	Title:	 	President and Chief Executive Officer
		
	Purchaser:	 	 Patriot Financial Partners, L.P.

Patriot Financial Partners Parallel, L.P.

			
		 	By:	 	 /s/ James J. Lynch

		 		 	Name:	 	James J. Lynch
		 		 	Title: Managing Partner

 IN WITNESS WHEREOF, the parties have executed this Agreement or caused their duly authorized
officers to execute this Agreement as of the date first written above. 
  

							
	The Corporation:	 	SQUARE 1 FINANCIAL, INC.
			
		 	By:	 	 /s/ Douglas H. Bowers

		 		 	Name:	 	Douglas Bowers
		 		 	Title:	 	President and Chief Executive Officer
		
	Purchaser:	 	 ENDICOTT OPPORTUNITY

PARTNERS III, L.P.

			
		 	By:	 	 /s/ Robert I. Usdan

		 		 	Name:	 	Robert I. Usdan
		 		 	Title: Managing Member – W.R. Endicott III,
		 		 	 L.L.C. – General Partner of Endicott

Opportunity Partners III, L.P.

 IN WITNESS WHEREOF, the parties have executed this Agreement or caused their duly authorized
officers to execute this Agreement as of the date first written above. 
  

							
	The Corporation:	 	SQUARE 1 FINANCIAL, INC.
			
		 	By:	 	 /s/ Douglas H. Bowers

		 		 	Name:	 	Douglas Bowers
		 		 	Title:	 	President and Chief Executive Officer
		
	Purchaser:	 	 CASTLE CREEK PARTNERS IV, L.P.

			
		 	By:	 	 /s/ John Pietrzak

		 		 	Name:	 	John Pietrzak
		 		 	Title: PrincipalExhibit 10.15

 Exhibit 10.15 

GUARANTEE AGREEMENT 

SQUARE 1 FINANCIAL, INC. 

Dated as of September 30, 2008 

 TABLE OF CONTENTS 

 

							
	ARTICLE I	  
	DEFINITIONS AND INTERPRETATION	  
			
	SECTION 1.1.	  	 Definitions and Interpretation.
	  	 	1	  
	
	ARTICLE II	  
	POWERS, DUTIES AND RIGHTS OF THE GUARANTEE TRUSTEE	  
			
	SECTION 2.1.	  	 Powers and Duties of the Guarantee Trustee.
	  	 	4	  
	SECTION 2.2.	  	 Certain Rights of the Guarantee Trustee.
	  	 	5	  
	SECTION 2.3.	  	 Not Responsible for Recitals or Issuance of Guarantee.
	  	 	7	  
	SECTION 2.4.	  	 Events of Default: Waiver.
	  	 	7	  
	SECTION 2.5.	  	 Events of Default: Notice.
	  	 	7	  
	
	ARTICLE III	  
	THE GUARANTEE TRUSTEE	  
			
	SECTION 3.1.	  	 The Guarantee Trustee: Eligibility.
	  	 	8	  
	SECTION 3.2.	  	 Appointment. Removal and Resignation of the Guarantee Trustee.
	  	 	8	  
	
	ARTICLE IV	  
	GUARANTEE	  
			
	SECTION 4.1.	  	 Guarantee.
	  	 	9	  
	SECTION 4.2.	  	 Waiver of Notice and Demand.
	  	 	9	  
	SECTION 4.3.	  	 Obligations Not Affected.
	  	 	10	  
	SECTION 4.4.	  	 Rights of Holders.
	  	 	10	  
	SECTION 4.5.	  	 Guarantee of Payment.
	  	 	11	  
	SECTION 4.6.	  	 Subrogation.
	  	 	11	  
	SECTION 4.7.	  	 Independent Obligations.
	  	 	11	  
	SECTION 4.8.	  	 Enforcement.
	  	 	11	  
	
	ARTICLE V	  
	LIMITATION OF TRANSACTIONS; SUBORDINATION	  
			
	SECTION 5.1.	  	 Limitation of Transactions.
	  	 	12	  
	SECTION 5.2.	  	 Ranking.
	  	 	12	  
	
	ARTICLE VI	  
	TERMINATION	  
			
	SECTION 6.1.	  	 Termination.
	  	 	13	  

  
 i 

							
	ARTICLE VII	  
	INDEMNIFICATION	  
			
	SECTION 7.1.	  	 Exculpation.
	  	 	13	  
	SECTION 7.2.	  	 Indemnification.
	  	 	13	  
	SECTION 7.3.	  	 Compensation: Reimbursement of Expenses.
	  	 	14	  
	
	ARTICLE VIII	  
	MISCELLANEOUS	  
			
	SECTION 8.1.	  	 Successors and Assigns.
	  	 	15	  
	SECTION 8.2.	  	 Amendments.
	  	 	15	  
	SECTION 8.3.	  	 Notices.
	  	 	15	  
	SECTION 8.4.	  	 Benefit.
	  	 	16	  
	SECTION 8.5.	  	 Governing Law.
	  	 	16	  
	SECTION 8.6.	  	 Counterparts.
	  	 	16	  

  
 ii 

 GUARANTEE AGREEMENT 

This GUARANTEE AGREEMENT (the “Guarantee”), dated as of September 30, 2008, is executed and delivered by Square 1
Financial, Inc., a bank holding company incorporated in the State of Delaware (the “Guarantor”), and Wilmington Trust Company, a Delaware banking corporation, as trustee (the “Guarantee Trustee”), for the benefit of the Holders
(as defined herein) from time to time of the Capital Securities (as defined herein) of Square 1 Financial Capital Trust I, a Delaware statutory trust (the “Issuer”). 

WHEREAS, pursuant to an Amended and Restated Declaration of Trust (the “Declaration”), dated as of September 30, 2008, among
the trustees named therein of the Issuer, Square 1 Financial, Inc., as sponsor, and the Holders from time to time of undivided beneficial interests in the assets of the Issuer, the Issuer is issuing on the date hereof securities, having an aggregate
liquidation amount of $7,415,000 (the “Capital Securities”); and 
 WHEREAS, as incentive for the Holders to purchase the Capital
Securities, the Guarantor desires irrevocably and unconditionally to agree, to the extent set forth in this Guarantee, to pay to the Holders of Capital Securities the Guarantee Payments (as defined herein) and to make certain other payments on the
terms and conditions set forth herein. 
 NOW, THEREFORE, in consideration of the purchase by each Holder of the Capital Securities, which
purchase the Guarantor hereby agrees shall benefit the Guarantor, the Guarantor executes and delivers this Guarantee for the benefit of the Holders. 

ARTICLE I 
 DEFINITIONS AND
INTERPRETATION 
  

	 	SECTION 1.1.	Definitions and Interpretation. 

 In this Guarantee, unless the context otherwise
requires: 
 (a) capitalized terms used in this Guarantee but not defined in the preamble above have the respective meanings assigned to
them in this Section 1.1; 
 (b) a term defined anywhere in this Guarantee has the same meaning throughout; 

(c) all references to “the Guarantee” or “this Guarantee” are to this Guarantee as modified, supplemented or amended from
time to time; 
 (d) all references in this Guarantee to Articles and Sections are to Articles and Sections of this Guarantee, unless
otherwise specified; 
 (e) terms defined in the Declaration as of the date of execution of this Guarantee have the same meanings when used
in this Guarantee, unless otherwise defined in this Guarantee or unless the context otherwise requires; and 
 (f) a reference to the
singular includes the plural and vice versa. 

  
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 “Beneficiaries” means any Person to whom the Issuer is or hereafter becomes indebted or
liable. 
 “Common Securities” has the meaning specified in the Declaration. 

“Corporate Trust Office” means the office of the Guarantee Trustee at which at any particular time its corporate trust business
shall be principally administered, which at all times shall be located within the United States and at the time of the execution of this Guarantee shall be Rodney Square North, 1100 North Market Street, Wilmington, DE 19890-0001. 

“Covered Person” means any Holder of Capital Securities. 

“Debenture Issuer” means Square 1 Financial, Inc. or any successor entity resulting from any consolidation, amalgamation, merger or
other business combination, in its capacity as issuer of the Debentures. 
 “Debentures” means the junior subordinated debentures
of the Debenture Issuer that are designated in the Indenture as the “Junior Subordinated Convertible Debt Securities due 2038” and held by the Institutional Trustee (as defined in the Declaration) of the Issuer. 

“Event of Default” has the meaning set forth in Section 2.4. 

“Guarantee Payments” means the following payments or distributions, without duplication, with respect to the Capital Securities, to
the extent not paid or made by the Issuer: (i) any accrued and unpaid Distributions (as defined in the Declaration) which are required to be paid on such Capital Securities to the extent the Issuer has funds available in the Property Account
(as defined in the Declaration) therefor at such time, (ii) the price payable upon the redemption of any Capital Securities to the extent the Issuer has funds available in the Property Account therefor at such time, with respect to any Capital
Securities that are (1) called for redemption by the Issuer or (2) mandatorily redeemed by the Issuer, in each case, in accordance with the terms of such Capital Securities, and (iii) upon a voluntary or involuntary liquidation,
dissolution, winding-up or termination of the Issuer (other than in connection with the distribution of Debentures to the Holders of the Capital Securities in exchange therefor as provided in the Declaration), the lesser of (a) the aggregate of
the liquidation amount of the Capital Securities and all accrued and unpaid Distributions on the Capital Securities to the date of payment, to the extent the Issuer has funds available in the Property Account therefor at such time, and (b) the
amount of assets of the Issuer remaining available for distribution to Holders in liquidation of the Issuer after satisfaction of liabilities to creditors of the Issuer as required by applicable law (in either case, the “Liquidation
Distribution”). 
 “Guarantee Trustee” means Wilmington Trust Company, until a Successor Guarantee Trustee has been appointed
and has accepted such appointment pursuant to the terms of this Guarantee and thereafter means each such Successor Guarantee Trustee. 

“Holder” means any Person in whose name any Capital Securities are registered on the books and records of the Issuer;
provided, however, that, in determining whether the holders of the requisite percentage of Capital Securities have given any request, notice, consent or waiver hereunder, “Holder” shall not include the Guarantor or any
Affiliate of the Guarantor. 

  
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 “Indemnified Person” means the Guarantee Trustee (including in its individual
capacity), any Affiliate of the Guarantee Trustee, or any officers, directors, shareholders, members, partners, employees, representatives, nominees, custodians or agents of the Guarantee Trustee. 

“Indenture” means the Indenture, dated as of September 30, 2008, between the Debenture Issuer and Wilmington Trust Company, not
in its individual capacity but solely as trustee, and any indenture supplemental thereto pursuant to which the Debentures are to be issued to the Institutional Trustee of the Issuer. 

“Liquidation Distribution” has the meaning set forth in the definition of “Guarantee Payments” herein. 

“Majority in liquidation amount of the Capital Securities” means Holder(s) of outstanding Capital Securities, voting together as a
class, but separately from the holders of Common Securities, of more than 50% of the aggregate liquidation amount (including the amount that would be paid upon the redemption, liquidation or otherwise on the date upon which the voting percentages
are determined, plus unpaid Distributions accrued thereon to such date) of all Capital Securities then outstanding. 

“Obligations” means any costs, expenses or liabilities (but not including liabilities related to taxes) of the Issuer, other than
obligations of the Issuer to pay to holders of any Trust Securities the amounts due such holders pursuant to the terms of the Trust Securities. 

“Officer’s Certificate” means, with respect to any Person, a certificate signed by one Authorized Officer of such Person. Any
Officer’s Certificate delivered with respect to compliance with a condition or covenant provided for in this Guarantee shall include: 

(a) a statement that such officer signing the Officer’s Certificate has read the covenant or condition and the definitions relating
thereto; 
 (b) a brief statement of the nature and scope of the examination or investigation undertaken by such officer in rendering the
Officer’s Certificate; 
 (c) a statement that such officer has made such examination or investigation as, in such officer’s
opinion, is necessary to enable such officer to express an informed opinion as to whether or not such covenant or condition has been complied with; and 

(d) a statement as to whether, in the opinion of such officer, such condition or covenant has been complied with. 

“Person” means a legal person, including any individual, corporation, estate, partnership, joint venture, association, joint stock
company, limited liability company, trust, unincorporated association, or government or any agency or political subdivision thereof, or any other entity of whatever nature. 

“Responsible Officer” means, with respect to the Guarantee Trustee, any officer within the Corporate Trust Office of the Guarantee
Trustee with direct responsibility for the administration of any matters relating to this Guarantee, including any vice president, any 

  
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assistant vice president, any secretary, any assistant secretary, the treasurer, any assistant treasurer, any trust officer or other officer of the Corporate Trust Office of the Guarantee Trustee
customarily performing functions similar to those performed by any of the above designated officers and also means, with respect to a particular corporate trust matter, any other officer to whom such matter is referred because of that officer’s
knowledge of and familiarity with the particular subject. 
 “Successor Guarantee Trustee” means a successor Guarantee Trustee
possessing the qualifications to act as Guarantee Trustee under Section 3.1. 
 “Trust Securities” means the Common
Securities and the Capital Securities. 
 ARTICLE II 

POWERS, DUTIES AND RIGHTS OF THE GUARANTEE TRUSTEE 
  

	 	SECTION 2.1.	Powers and Duties of the Guarantee Trustee. 

 (a) This Guarantee shall be held by the
Guarantee Trustee for the benefit of the Holders of the Capital Securities, and the Guarantee Trustee shall not transfer this Guarantee to any Person except a Holder of Capital Securities exercising his or her rights pursuant to Section 4.4
(b) or to a Successor Guarantee Trustee on acceptance by such Successor Guarantee Trustee of its appointment to act as Successor Guarantee Trustee. The right, title and interest of the Guarantee Trustee shall automatically vest in any Successor
Guarantee Trustee, and such vesting and cessation of title shall be effective whether or not conveyancing documents have been executed and delivered pursuant to the appointment of such Successor Guarantee Trustee. 

(b) If an Event of Default actually known to a Responsible Officer of the Guarantee Trustee has occurred and is continuing, the Guarantee
Trustee shall enforce this Guarantee for the benefit of the Holders of the Capital Securities. 
 (c) The Guarantee Trustee, before the
occurrence of any Event of Default and after the curing or waiving of all Events of Default that may have occurred, shall undertake to perform only such duties as are specifically set forth in this Guarantee, and no implied covenants shall be read
into this Guarantee against the Guarantee Trustee. In case an Event of Default has occurred (that has not been cured or waived pursuant to Section 2.4(b)) and is actually known to a Responsible Officer of the Guarantee Trustee, the Guarantee
Trustee shall exercise such of the rights and powers vested in it by this Guarantee, and use the same degree of care and skill in its exercise thereof, as a prudent person would exercise or use under the circumstances in the conduct of his or her
own affairs. 

  
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 (d) No provision of this Guarantee shall be construed to relieve the Guarantee Trustee from
liability for its own negligent action, its own negligent failure to act, or its own willful misconduct or bad faith, except that: 

(i) prior to the occurrence of any Event of Default and after the curing or waiving of all Events of Default that may have
occurred: 
 (A) the duties and obligations of the Guarantee Trustee shall be determined solely by the express provisions of
this Guarantee, and the Guarantee Trustee shall not be liable except for the performance of such duties and obligations as are specifically set forth in this Guarantee, and no implied covenants or obligations shall be read into this Guarantee
against the Guarantee Trustee; and 
 (B) in the absence of bad faith on the part of the Guarantee Trustee, the Guarantee
Trustee may conclusively rely, as to the truth of the statements and the correctness of the opinions expressed therein, upon any certificates or opinions furnished to the Guarantee Trustee and conforming to the requirements of this Guarantee; but in
the case of any such certificates or opinions furnished to the Guarantee Trustee, the Guarantee Trustee shall be under a duty to examine the same to determine whether or not on their face they conform to the requirements of this Guarantee; 

(ii) the Guarantee Trustee shall not be liable for any error of judgment made in good faith by a Responsible Officer of the
Guarantee Trustee, unless it shall be proved that such Responsible Officer of the Guarantee Trustee or the Guarantee Trustee was negligent in ascertaining the pertinent facts upon which such judgment was made; 

(iii) the Guarantee Trustee shall not be liable with respect to any action taken or omitted to be taken by it in good faith in
accordance with the written direction of the Holders of a Majority in liquidation amount of the Capital Securities relating to the time, method and place of conducting any proceeding for any remedy available to the Guarantee Trustee, or exercising
any trust or power conferred upon the Guarantee Trustee under this Guarantee; and 
 (iv) no provision of this Guarantee
shall require the Guarantee Trustee to expend or risk its own funds or otherwise incur personal financial liability in the performance of any of its duties or in the exercise of any of its rights or powers, if the Guarantee Trustee shall have
reasonable grounds for believing that the repayment of such funds is not reasonably assured to it under the terms of this Guarantee, or security and indemnity, reasonably satisfactory to the Guarantee Trustee, against such risk or liability is not
reasonably assured to it. 
  

	 	SECTION 2.2.	Certain Rights of the Guarantee Trustee. 

 (a) Subject to the provisions of
Section 2.1: 
 (i) The Guarantee Trustee may conclusively rely, and shall be fully protected in acting or refraining
from acting upon, any resolution, certificate, statement, instrument, opinion, report, notice, request, direction, consent, order, bond, debenture, note, other evidence of indebtedness or other paper or document believed by it to be genuine and to
have been signed, sent or presented by the proper party or parties. 
 (ii) Any direction or act of the Guarantor
contemplated by this Guarantee shall be sufficiently evidenced by an Officer’s Certificate. 

  
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 (iii) Whenever, in the administration of this Guarantee, the Guarantee Trustee
shall deem it desirable that a matter be proved or established before taking, suffering or omitting any action hereunder, the Guarantee Trustee (unless other evidence is herein specifically prescribed) may, in the absence of bad faith on its part,
request and conclusively rely upon an Officer’s Certificate of the Guarantor which, upon receipt of such request, shall be promptly delivered by the Guarantor. 

(iv) The Guarantee Trustee shall have no duty to see to any recording, filing or registration of any instrument or other
writing (or any rerecording, refiling or reregistration thereof). 
 (v) The Guarantee Trustee may consult with counsel of
its selection, and the advice or opinion of such counsel with respect to legal matters shall be full and complete authorization and protection in respect of any action taken, suffered or omitted by it hereunder in good faith and in accordance with
such advice or opinion. Such counsel may be counsel to the Guarantor or any of its Affiliates and may include any of its employees. The Guarantee Trustee shall have the right at any time to seek instructions concerning the administration of this
Guarantee from any court of competent jurisdiction. 
 (vi) The Guarantee Trustee shall be under no obligation to exercise
any of the rights or powers vested in it by this Guarantee at the request or direction of any Holder, unless such Holder shall have provided to the Guarantee Trustee such security and indemnity, reasonably satisfactory to the Guarantee Trustee,
against the costs, expenses (including attorneys’ fees and expenses and the expenses of the Guarantee Trustee’s agents, nominees or custodians) and liabilities that might be incurred by it in complying with such request or direction,
including such reasonable advances as may be requested by the Guarantee Trustee; provided, however, that nothing contained in this Section 2.2(a)(vi) shall be taken to relieve the Guarantee Trustee, upon the occurrence of an Event of Default,
of its obligation to exercise the rights and powers vested in it by this Guarantee. 
 (vii) The Guarantee Trustee shall not
be bound to make any investigation into the facts or matters stated in any resolution, certificate, statement, instrument, opinion, report, notice, request, direction, consent, order, bond, debenture, note, other evidence of indebtedness or other
paper or document, but the Guarantee Trustee, in its discretion, may make such further inquiry or investigation into such facts or matters as it may see fit. 

(viii) The Guarantee Trustee may execute any of the trusts or powers hereunder or perform any duties hereunder either directly
or by or through agents, nominees, custodians or attorneys, and the Guarantee Trustee shall not be responsible for any misconduct or negligence on the part of any agent or attorney appointed with due care by it hereunder. 

(ix) Any action taken by the Guarantee Trustee or its agents hereunder shall bind the Holders of the Capital Securities, and
the signature of the Guarantee Trustee or its agents alone shall be sufficient and effective to perform any such action. No third party shall be required to inquire as to the authority of the Guarantee Trustee to so act or

  
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as to its compliance with any of the terms and provisions of this Guarantee, both of which shall be conclusively evidenced by the Guarantee Trustee’s or its agent’s taking such action.

 (x) Whenever in the administration of this Guarantee the Guarantee Trustee shall deem it desirable to receive instructions
with respect to enforcing any remedy or right or taking any other action hereunder, the Guarantee Trustee (A) may request instructions from the Holders of a Majority in liquidation amount of the Capital Securities, (B) may refrain from
enforcing such remedy or right or taking such other action until such instructions are received and (C) shall be protected in conclusively relying on or acting in accordance with such instructions. 

(xi) The Guarantee Trustee shall not be liable for any action taken, suffered, or omitted to be taken by it in good faith and
reasonably believed by it to be authorized or within the discretion or rights or powers conferred upon it by this Guarantee. 
 (b) No
provision of this Guarantee shall be deemed to impose any duty or obligation on the Guarantee Trustee to perform any act or acts or exercise any right, power, duty or obligation conferred or imposed on it, in any jurisdiction in which it shall be
illegal or in which the Guarantee Trustee shall be unqualified or incompetent in accordance with applicable law to perform any such act or acts or to exercise any such right, power, duty or obligation. No permissive power or authority available to
the Guarantee Trustee shall be construed to be a duty. 
  

	 	SECTION 2.3.	Not Responsible for Recitals or Issuance of Guarantee. 

 The recitals contained in this
Guarantee shall be taken as the statements of the Guarantor, and the Guarantee Trustee does not assume any responsibility for their correctness. The Guarantee Trustee makes no representation as to the validity or sufficiency of this Guarantee. 

 

	 	SECTION 2.4.	Events of Default: Waiver. 

 (a) An “Event of Default” under this Guarantee
will occur upon the failure of the Guarantor to perform any of its payment or other obligations hereunder. 
 (b) The Holders of a Majority
in liquidation amount of the Capital Securities may, voting or consenting as a class, on behalf of the Holders of all of the Capital Securities, waive any past Event of Default and its consequences. Upon such waiver, any such Event of Default shall
cease to exist, and shall be deemed to have been cured, for every purpose of this Guarantee, but no such waiver shall extend to any subsequent or other default or Event of Default or impair any right consequent thereon. 

 

	 	SECTION 2.5.	Events of Default: Notice. 

 (a) The Guarantee Trustee shall, within 90 days after the
occurrence of an Event of Default, transmit by mail, first class postage prepaid, to the Holders of the Capital Securities, notices of all Events of Default actually known to a Responsible Officer of the Guarantee Trustee, unless such defaults have
been cured before the giving of such notice, provided, however, that the Guarantee Trustee shall be protected in withholding such notice if and so long as a Responsible Officer of the Guarantee Trustee in good faith determines that the withholding
of such notice is in the interests of the Holders of the Capital Securities. 

  
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 (b) The Guarantee Trustee shall not be charged with knowledge of any Event of Default unless the
Guarantee Trustee shall have received written notice thereof from the Guarantor or a Holder of the Capital Securities, or a Responsible Officer of the Guarantee Trustee charged with the administration of this Guarantee shall have actual knowledge
thereof. 
 ARTICLE III 
 THE
GUARANTEE TRUSTEE 
  

	 	SECTION 3.1.	The Guarantee Trustee: Eligibility. 

 (a) There shall at all times be a Guarantee Trustee
which shall: 
 (i) not be an Affiliate of the Guarantor; and 

(ii) be a corporation or national association organized and doing business under the laws of the United States of America or
any state thereof or of the District of Columbia, or Person authorized under such laws to exercise corporate trust powers, having a combined capital and surplus of at least 50 million U.S. dollars ($50,000,000), and subject to supervision or
examination by federal, state or District of Columbia authority. If such corporation or national association publishes reports of condition at least annually, pursuant to law or to the requirements of the supervising or examining authority referred
to above, then, for the purposes of this Section 3.1 (a)(ii), the combined capital and surplus of such corporation or national association shall be deemed to be its combined capital and surplus as set forth in its most recent report of
condition so published. 
 (b) If at any time the Guarantee Trustee shall cease to be eligible to so act under Section 3.1(a), the
Guarantee Trustee shall immediately resign in the manner and with the effect set forth in Section 3.2(c). 
 (c) If the Guarantee
Trustee has or shall acquire any “conflicting interest” within the meaning of Section 310(b) of the Trust Indenture Act, the Guarantee Trustee shall either eliminate such interest or resign to the extent and in the manner provided by,
and subject to, this Guarantee. 
  

	 	SECTION 3.2.	Appointment. Removal and Resignation of the Guarantee Trustee. 

 (a) Subject to
Section 3.2(b), the Guarantee Trustee may be appointed or removed without cause at any time by the Guarantor except during an Event of Default. 

(b) The Guarantee Trustee shall not be removed in accordance with Section 3.2(a) until a Successor Guarantee Trustee has been appointed
and has accepted such appointment by written instrument executed by such Successor Guarantee Trustee and delivered to the Guarantor. 

  
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 (c) The Guarantee Trustee appointed to office shall hold office until a Successor Guarantee
Trustee shall have been appointed or until its removal or resignation. The Guarantee Trustee may resign from office (without need for prior or subsequent accounting) by an instrument in writing executed by the Guarantee Trustee and delivered to the
Guarantor, which resignation shall not take effect until a Successor Guarantee Trustee has been appointed and has accepted such appointment by an instrument in writing executed by such Successor Guarantee Trustee and delivered to the Guarantor and
the resigning Guarantee Trustee. 
 (d) If no Successor Guarantee Trustee shall have been appointed and accepted appointment as provided in
this Section 3.2 within 60 days after delivery of an instrument of removal or resignation, the Guarantee Trustee resigning or being removed may petition any court of competent jurisdiction for appointment of a Successor Guarantee Trustee. Such
court may thereupon, after prescribing such notice, if any, as it may deem proper, appoint a Successor Guarantee Trustee. 
 (e) No
Guarantee Trustee shall be liable for the acts or omissions to act of any Successor Guarantee Trustee. 
 (f) Upon termination of this
Guarantee or removal or resignation of the Guarantee Trustee pursuant to this Section 3.2, the Guarantor shall pay to the Guarantee Trustee all amounts owing to the Guarantee Trustee under Sections 7.2 and 7.3 accrued to the date of such
termination, removal or resignation. 
 ARTICLE IV 

GUARANTEE 
  

	 	SECTION 4.1.	Guarantee. 

 (a) The Guarantor irrevocably and unconditionally agrees to pay in full to
the Holders the Guarantee Payments (without duplication of amounts theretofore paid by the Issuer), as and when due, regardless of any defense (except defense of payment by the Issuer), right of set-off or counterclaim that the Issuer may have or
assert. The Guarantor’s obligation to make a Guarantee Payment may be satisfied by direct payment of the required amounts by the Guarantor to the Holders or by causing the Issuer to pay such amounts to the Holders. 

(b) The Guarantor hereby also agrees to assume any and all Obligations of the Issuer and in the event any such Obligation is not so assumed,
subject to the terms and conditions hereof, the Guarantor hereby irrevocably and unconditionally guarantees to each Beneficiary the full payment, when and as due, of any and all Obligations to such Beneficiaries. This Guarantee is intended to be for
the Beneficiaries who have received notice hereof. 
  

	 	SECTION 4.2.	Waiver of Notice and Demand. 

 The Guarantor hereby waives notice of acceptance of this
Guarantee and of any liability to which it applies or may apply, presentment, demand for payment, any right to require a proceeding first against the Issuer or any other Person before proceeding against the Guarantor, protest, notice of nonpayment,
notice of dishonor, notice of redemption and all other notices and demands. 

  
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	 	SECTION 4.3.	Obligations Not Affected. 

 The obligations, covenants, agreements and duties of the
Guarantor under this Guarantee shall in no way be affected or impaired by reason of the happening from time to time of any of the following: 

(a) the release or waiver, by operation of law or otherwise, of the performance or observance by the Issuer of any express or implied
agreement, covenant, term or condition relating to the Capital Securities to be performed or observed by the Issuer; 
 (b) the extension of
time for the payment by the Issuer of all or any portion of the Distributions, the price payable upon the redemption of the Capital Securities, the Liquidation Distribution or any other sums payable under the terms of the Capital Securities or the
extension of time for the performance of any other obligation under, arising out of, or in connection with, the Capital Securities (other than an extension of time for the payment of the Distributions, the price payable upon the redemption of the
Capital Securities, the Liquidation Distribution or other sums payable that results from the extension of any interest payment period on the Debentures); 

(c) any failure, omission, delay or lack of diligence on the part of the Holders to enforce, assert or exercise any right, privilege, power or
remedy conferred on the Holders pursuant to the terms of the Capital Securities, or any action on the part of the Issuer granting indulgence or extension of any kind; 

(d) the voluntary or involuntary liquidation, dissolution, sale of any collateral, receivership, insolvency, bankruptcy, assignment for the
benefit of creditors, reorganization, arrangement, composition or readjustment of debt of, or other similar proceedings affecting, the Issuer or any of the assets of the Issuer; 

(e) any invalidity of, or defect or deficiency in, the Capital Securities; 

(f) the settlement or compromise of any obligation guaranteed hereby or hereby incurred; or 

(g) any other circumstance whatsoever that might otherwise constitute a legal or equitable discharge or defense of a guarantor, it being the
intent of this Section 4.3 that the obligations of the Guarantor hereunder shall be absolute and unconditional under any and all circumstances. 

There shall be no obligation of the Holders to give notice to, or obtain consent of, the Guarantor with respect to the happening of any of the
foregoing. 
  

	 	SECTION 4.4.	Rights of Holders. 

 (a) The Holders of a Majority in liquidation amount of the Capital
Securities have the right to direct the time, method and place of conducting any proceeding for any remedy available to the Guarantee Trustee in respect of this Guarantee or to direct the exercise of any trust or power conferred upon the Guarantee
Trustee under this Guarantee; provided, however, that (subject to Sections 2.1 and 2.2) the Guarantee Trustee shall have the right to decline to follow 

  
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any such direction if the Guarantee Trustee shall determine that the actions so directed would be unjustly prejudicial to the Holders not taking part in such direction or if the Guarantee Trustee
being advised by legal counsel determines that the action or proceeding so directed may not lawfully be taken or if the Guarantee Trustee in good faith by its board of directors or trustees, executive committee or a trust committee of directors or
trustees and/or Responsible Officers shall determine that the action or proceeding so directed would involve the Guarantee Trustee in personal liability. 

(b) Any Holder of Capital Securities may institute a legal proceeding directly against the Guarantor to enforce the Guarantee Trustee’s
rights under this Guarantee, without first instituting a legal proceeding against the Issuer, the Guarantee Trustee or any other Person. The Guarantor waives any right or remedy to require that any such action be brought first against the Issuer,
the Guarantee Trustee or any other Person before so proceeding directly against the Guarantor. 
  

	 	SECTION 4.5.	Guarantee of Payment. 

 This Guarantee creates a guarantee of payment and not of
collection. 
  

	 	SECTION 4.6.	Subrogation. 

 The Guarantor shall be subrogated to all (if any) rights of the Holders of
Capital Securities against the Issuer in respect of any amounts paid to such Holders by the Guarantor under this Guarantee; provided, however, that the Guarantor shall not (except to the extent required by applicable provisions of law) be entitled
to enforce or exercise any right that it may acquire by way of subrogation or any indemnity, reimbursement or other agreement, in all cases as a result of payment under this Guarantee, if, after giving effect to any such payment, any amounts are due
and unpaid under this Guarantee. If any amount shall be paid to the Guarantor in violation of the preceding sentence, the Guarantor agrees to hold such amount in trust for the Holders and to pay over such amount to the Holders. 

 

	 	SECTION 4.7.	Independent Obligations. 

 The Guarantor acknowledges that its obligations hereunder are
independent of the obligations of the Issuer with respect to the Capital Securities and that the Guarantor shall be liable as principal and as debtor hereunder to make Guarantee Payments pursuant to the terms of this Guarantee notwithstanding the
occurrence of any event referred to in subsections (a) through (g), inclusive, of Section 4.3 hereof. 
  

	 	SECTION 4.8.	Enforcement. 

 A Beneficiary may enforce the Obligations of the Guarantor contained in
Section 4.1 (b) directly against the Guarantor, and the Guarantor waives any right or remedy to require that any action be brought against the Issuer or any other person or entity before proceeding against the Guarantor. 

The Guarantor shall be subrogated to all rights (if any) of any Beneficiary against the Issuer in respect of any amounts paid to the
Beneficiaries by the Guarantor under this Guarantee; 

  
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provided, however, that the Guarantor shall not (except to the extent required by applicable provisions of law) be entitled to enforce or exercise any rights that it may acquire by way of
subrogation or any indemnity, reimbursement or other agreement, in all cases as a result of payment under this Guarantee, if, after giving effect to such payment, any amounts are due and unpaid under this Guarantee. If any amount shall be paid to
the Guarantor in violation of the preceding sentence, the Guarantor agrees to hold such amount in trust for the Beneficiaries and to pay over such amount to the Beneficiaries. 

ARTICLE V 
 LIMITATION OF
TRANSACTIONS; SUBORDINATION 
  

	 	SECTION 5.1.	Limitation of Transactions. 

 So long as any Capital Securities remain outstanding, if
(a) there shall have occurred and be continuing an Event of Default or (b) Debenture Issuer shall have selected an Extension Period as provided in the Indenture and such period, or any extension thereof, shall have commenced and be
continuing, then the Guarantor may not (x) declare or pay any dividends or distributions on, or redeem, purchase, acquire, or make a liquidation payment with respect to, any of the Guarantor’s capital stock, (y) make any payment of
principal of or interest or premium, if any, on or repay, repurchase or redeem any debt securities of the Guarantor that rank in all respects pari passu with or junior in interest to the Debentures or (z) make any payment under any
guarantees of the Guarantor that rank in all respects pari passu with or junior in interest to this Guarantee (other than (i) repurchases, redemptions or other acquisitions of shares of capital stock of the Guarantor (A) in
connection with any employment contract, benefit plan or other similar arrangement with or for the benefit of one or more employees, officers, directors, or consultants, (B) in connection with a dividend reinvestment or stockholder stock
purchase plan or (C) in connection with the issuance of capital stock of the Guarantor (or securities convertible into or exercisable for such capital stock), as consideration in an acquisition transaction entered into prior to the occurrence
of the Event of Default or the applicable Extension Period, (ii) as a result of any exchange or conversion of any class or series of the Guarantor’s capital stock (or any capital stock of a subsidiary of the Guarantor) for any class or
series of the Guarantor’s capital stock or of any class or series of the Guarantor’s indebtedness for any class or series of the Guarantor’s capital stock, (iii) the purchase of fractional interests in shares of the
Guarantor’s capital stock pursuant to the conversion or exchange provisions of such capital stock or the security being converted or exchanged, (iv) any declaration of a dividend in connection with any stockholder’s rights plan, or
the issuance of rights, stock or other property under any stockholder’s rights plan, or the redemption or repurchase of rights pursuant thereto, or (v) any dividend in the form of stock, warrants, options or other rights where the dividend
stock or the stock issuable upon exercise of such warrants, options or other rights is the same stock as that on which the dividend is being paid or ranks pari passu with or junior in interest to such stock). 

 

	 	SECTION 5.2.	Ranking. 

 This Guarantee will constitute an unsecured obligation of the Guarantor and
will rank subordinate and junior in right of payment to all present and future Senior Indebtedness (as defined in the Indenture) of the Guarantor. By their acceptance thereof, each Holder of Capital Securities agrees to the foregoing provisions of
this Guarantee and the other terms set forth herein. 

  
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 ARTICLE VI 

TERMINATION 
  

	 	SECTION 6.1.	Termination. 

 This Guarantee shall terminate as to the Capital Securities (i) upon
full payment of the price payable upon redemption of all Capital Securities then outstanding, (ii) upon the distribution of all of the Debentures to the Holders of all of the Capital Securities or (iii) upon full payment of the amounts
payable in accordance with the Declaration upon dissolution of the Issuer. This Guarantee will continue to be effective or will be reinstated, as the case may be, if at any time any Holder of Capital Securities must restore payment of any sums paid
under the Capital Securities or under this Guarantee. 
 ARTICLE VII 

INDEMNIFICATION 
  

	 	SECTION 7.1.	Exculpation. 

 (a) No Indemnified Person shall be liable, responsible or accountable in
damages or otherwise to the Guarantor or any Covered Person for any loss, damage or claim incurred by reason of any act or omission of such Indemnified Person in good faith in accordance with this Guarantee and in a manner that such Indemnified
Person reasonably believed to be within the scope of the authority conferred on such Indemnified Person by this Guarantee or by law, except that an Indemnified Person shall be liable for any such loss, damage or claim incurred by reason of such
Indemnified Person’s negligence, willful misconduct or bad faith with respect to such acts or omissions. 
 (b) An Indemnified Person
shall be fully protected in relying in good faith upon the records of the Issuer or the Guarantor and upon such information, opinions, reports or statements presented to the Issuer or the Guarantor by any Person as to matters the Indemnified Person
reasonably believes are within such other Person’s professional or expert competence and who, if selected by such Indemnified Person, has been selected with reasonable care by such Indemnified Person, including information, opinions, reports or
statements as to the value and amount of the assets, liabilities, profits, losses, or any other facts pertinent to the existence and amount of assets from which Distributions to Holders of Capital Securities might properly be paid. 

 

	 	SECTION 7.2.	Indemnification. 

 (a) The Guarantor agrees to indemnify each Indemnified Person for, and
to hold each Indemnified Person harmless against, any and all loss, liability, damage, claim or expense incurred without negligence, willful misconduct or bad faith on the part of the Indemnified Person, arising out of or in connection with the
acceptance or administration of the trust or trusts hereunder, including but not limited to the costs and expenses (including reasonable legal fees and expenses) of the Indemnified Person defending itself against, or investigating, any claim or

  
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liability in connection with the exercise or performance of any of the Indemnified Person’s powers or duties hereunder. The obligation to indemnify as set forth in this Section 7.2
shall survive the resignation or removal of the Guarantee Trustee and the termination of this Guarantee. 
 (b) Promptly after receipt by an
Indemnified Person under this Section 7.2 of notice of the commencement of any action, such Indemnified Person will, if a claim in respect thereof is to be made against the Guarantor under this Section 7.2, notify the Guarantor in writing
of the commencement thereof; but the failure so to notify the Guarantor (i) will not relieve the Guarantor from liability under paragraph (a) above unless and to the extent that the Guarantor did not otherwise learn of such action and such
failure results in the forfeiture by the Guarantor of substantial rights and defenses and (ii) will not, in any event, relieve the Guarantor from any obligations to any Indemnified Person other than the indemnification obligation provided in
paragraph (a) above. The Guarantor shall be entitled to appoint counsel of the Guarantor’s choice at the Guarantor’s expense to represent the Indemnified Person in any action for which indemnification is sought (in which case the
Guarantor shall not thereafter be responsible for the fees and expenses of any separate counsel retained by the Indemnified Person or Persons except as set forth below); provided, however, that such counsel shall be satisfactory to the Indemnified
Person. Notwithstanding the Guarantor’s election to appoint counsel to represent the Indemnified Person in any action, the Indemnified Person shall have the right to employ separate counsel (including local counsel), and the Guarantor shall
bear the reasonable fees, costs and expenses of such separate counsel, if (i) the use of counsel chosen by the Guarantor to represent the Indemnified Person would present such counsel with a conflict of interest, (ii) the actual or
potential defendants in, or targets of, any such action include both the Indemnified Person and the Guarantor and the Indemnified Person shall have reasonably concluded that there may be legal defenses available to it and/or other Indemnified
Persons which are different from or additional to those available to the Guarantor, (iii) the Guarantor shall not have employed counsel satisfactory to the Indemnified Person to represent the Indemnified Person within a reasonable time after
notice of the institution of such action or (iv) the Guarantor shall authorize the Indemnified Person to employ separate counsel at the expense of the Guarantor. The Guarantor will not, without the prior written consent of the Indemnified
Persons, settle or compromise or consent to the entry of any judgment with respect to any pending or threatened claim, action, suit or proceeding in respect of which indemnification or contribution may be sought hereunder (whether or not the
Indemnified Persons are actual or potential parties to such claim or action) unless such settlement, compromise or consent includes an unconditional release of each Indemnified Person from all liability arising out of such claim, action, suit or
proceeding. 
  

	 	SECTION 7.3.	Compensation: Reimbursement of Expenses. 

 The Guarantor agrees: 

(a) to pay to the Guarantee Trustee from time to time such compensation for all services rendered by it hereunder as the parties shall agree
to from time to time (which compensation shall not be limited by any provision of law in regard to the compensation of a trustee of an express trust); and 

  
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 (b) except as otherwise expressly provided herein, to reimburse the Guarantee Trustee upon
request for all reasonable expenses, disbursements and advances incurred or made by it in accordance with any provision of this Guarantee (including the reasonable compensation and the expenses and disbursements of its agents and counsel), except
any such expense, disbursement or advance as may be attributable to the negligence, willful misconduct or bad faith of the Guarantee Trustee. 

The provisions of this Section 7.3 shall survive the resignation or removal of the Guarantee Trustee and the termination of this
Guarantee. 
 ARTICLE VIII 

MISCELLANEOUS 
  

	 	SECTION 8.1.	Successors and Assigns. 

 All guarantees and agreements contained in this Guarantee shall
bind the successors, assigns, receivers, trustees and representatives of the Guarantor and shall inure to the benefit of the Holders of the Capital Securities then outstanding. Except in connection with any merger or consolidation of the Guarantor
with or into another entity or any sale, transfer or lease of the Guarantor’s assets to another entity, in each case to the extent permitted under the Indenture, the Guarantor may not assign its rights or delegate its obligations under this
Guarantee without the prior approval of the Holders of a Majority in liquidation amount of the Capital Securities. 
  

	 	SECTION 8.2.	Amendments. 

 Except with respect to any changes that do not adversely affect the powers,
preferences, rights or interests of Holders of the Capital Securities in any material respect (in which case no approval of Holders will be required), this Guarantee may be amended only with the prior approval of the Holders of a Majority in
liquidation amount of the Capital Securities. The provisions of the Declaration with respect to amendments thereof shall apply equally with respect to amendments of the Guarantee. 

 

	 	SECTION 8.3.	Notices. 

 All notices provided for in this Guarantee shall be in writing, duly signed by
the party giving such notice, and shall be delivered, telecopied or mailed by first class mail, as follows: 
 (a) if given to the Guarantee
Trustee, at the Guarantee Trustee’s mailing address set forth below (or such other address as the Guarantee Trustee may give notice of to the Holders of the Capital Securities): Wilmington Trust Company, Rodney Square North, 1100 North Market
Street, Wilmington, Delaware 19890-0001, Attention: Corporate Capital Markets, Telecopy: 302-636-4140, Telephone: 302-636-6000; 
 (b) if
given to the Guarantor, at the Guarantor’s mailing address set forth below (or such other address as the Guarantor may give notice of to the Holders of the Capital Securities and to the Guarantee Trustee): Square 1 Financial, Inc., 406
Blackwell Street, Crowe Building, Suite 240, Durham, North Carolina 27701, Attention: Richard J. Casey, Telecopy: (919) 314-3080, Telephone: (919) 314-3040; or 

  
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 (c) if given to any Holder of the Capital Securities, at the address set forth on the books and
records of the Issuer. 
 All such notices shall be deemed to have been given when received in person, telecopied with receipt confirmed, or
mailed by first class mail, postage prepaid, except that if a notice or other document is refused delivery or cannot be delivered because of a changed address of which no notice was given, such notice or other document shall be deemed to have been
delivered on the date of such refusal or inability to deliver. 
  

	 	SECTION 8.4.	Benefit. 

 This Guarantee is solely for the benefit of the Holders of the Capital
Securities and, subject to Section 2.1 (a), is not separately transferable from the Capital Securities. 
  

	 	SECTION 8.5.	Governing Law. 

 THIS GUARANTEE SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH,
THE LAWS OF THE STATE OF NEW YORK WITHOUT REGARD TO CONFLICT OF LAW PRINCIPLES OF SAID STATE OTHER THAN SECTION 5-1401 OF THE NEW YORK GENERAL OBLIGATIONS LAW. 
  

	 	SECTION 8.6.	Counterparts. 

 This Guarantee may contain more than one counterpart of the signature
page and this Guarantee may be executed by the affixing of the signature of the Guarantor and the Guarantee Trustee to any of such counterpart signature pages. All of such counterpart signature pages shall be read as though one, and they shall have
the same force and effect as though all of the signers had signed a single signature page. 
 THIS GUARANTEE is executed as of the day and
year first above written. 
  

					
	SQUARE 1 FINANCIAL, INC.,
	as Guarantor
		
	By:	 	 /s/ Richard J. Casey

		 	Name:	 	Richard J. Casey
		 	Title:	 	President and Chief Executive Officer
	
	 WILMINGTON TRUST COMPANY

as Guarantee Trustee

		
	By:	 	 /s/ Lori L. Donahue

		 	Name:	 	Lori L. Donahue
		 	Title:	 	Assistant Vice President

  
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