Century City’s PacWest Bancorp received final approval from federal regulators late Tuesday for its $231 million stock acquisition of Westlake Village’s First California Financial Group Inc.

The merger of First California, the parent of First California Bank, with PacWest, the holding company for Pacific Western Bank, is expected to close by May 31. The conversion of First California branches to PacWest branches is expected to be completed by June 14.

The all-stock deal represents a 19 percent premium over First California’s Nov. 6 closing price, the day before the deal was announced.

The merger will create the eighth largest publicly held bank headquartered in California. PacWest, with $5.4 billion in assets, has 66 branches from San Francisco to San Bernardino counties. First California Bank is a 15-branch institution with $1.9 billion in assets serving Southern California from San Luis Obispo to San Diego counties.

The banks have not indicated if some branches will close in the merger. Both operate branches in Glendale while First California has a branch at its former headquarters in Westlake Village, near a PacWest branch in Thousand Oaks.

In Wednesday trading on the Nasdaq, PacWest shares closed down 20 cents, about 1 percent, to $28.07. First California shares closed up 10 cents, about 1 percent, to $8.29.