X0306 4 2015-10-06 1 0001329799 SQUARE 1 FINANCIAL INC SQBK 0001603621 Thompson Gregory Bruce 406 BLACKWELL STREET SUITE 240 DURHAM NC 27701 0 1 0 0 EVP -- Shared Services Class A Common Stock 2015-10-06 4 D 0 35922 D 0 D Stock Option (Right to Buy) 6.0000 2015-10-06 4 D 0 8000 D Class A Common Stock 8000 0 D Restricted Stock Units 2015-10-06 4 D 0 7855 D Class A Common Stock 7855 0 D On October 6, 2015, pursuant to the Agreement and Plan of Merger, dated March 1, 2015, between PacWest Bancorp ("PacWest") and Square 1 Financial, Inc. ("Square 1"), Square 1 merged with and into PacWest, and each outstanding share of Square 1 common stock was converted into the right to receive 0.5997 of a share of PacWest common stock, with cash paid in lieu of fractional shares at a rate of $42.7827 per share (the "Average Closing Price"). At the effective time of the merger, each outstanding option to acquire shares of Square 1 common stock, whether vested or unvested, was cancelled and entitles the holder to receive an amount in cash equal to the product of (i) the total number of shares of Square 1 common stock subject to such option and (ii) the excess, if any, of (A) the product of (1) the Average Closing Price and (2) 0.5997 over (B) the exercise price per share of Square 1 common stock underlying such option, less any applicable taxes to be withheld with respect to such payment. Each outstanding restricted stock unit issued under Square 1's stock plan, whether vested or unvested, was cancelled and entitles the holder to receive an amount in cash equal to the product of (i) the number of shares of Square 1 common stock subject to such restricted stock unit award and (ii) the product of (A) the Average Closing Price and (B) 0.5997. In connection with the merger, the reporting person has the right to receive 21,542 shares of PacWest common stock and $358,788.56 in cash, subject to any required tax withholding under applicable law. On October 6, 2015, the effective date of the merger, the closing price of PacWest common stock was $43.97 per share. These stock options and restricted stock units were cancelled at the effective time of the merger and converted into the right to receive the consideration as described in notes (1) and (2) above. These shares are held in a joint account of Gregory B. Thompson and Kimberlie A. Thompson. Leah Webb, Attorney-in-Fact 2015-10-08