U.S. bank stocks outperformed the broader market in August.

The S&P U.S. BMI Banks index had a total return of 5.2% from July 30 to Aug. 31, topping the S&P 500's 3.0% increase. The median monthly return for the 209 banks in the S&P Global Market Intelligence analysis was 4.4%. Just 25 of the banks, including Wells Fargo & Co., recorded a negative return in August.

Waterbury, Conn.-based Webster Financial Corp. and Pearl River, N.Y.-based Sterling Bancorp, which announced a merger of equals on April 19, both returned more than 5% in August. Webster has consistently traded at a double-digit percentage point premium to the industry median in terms of price-to-adjusted tangible book value. Sterling Bancorp, on the other hand, has more closely tracked the industry median.

Click here to see S&P Global Market Intelligence's calculations for price-to-adjusted tangible book value as of Aug. 31.

Philadelphia-based Republic First Bancorp Inc. had the weakest market performance among the 209 banks, with a negative 9.5% return. It traded at 72.9% of adjusted tangible book value at Aug. 31, representing the lowest valuation in the analysis. In the previous month, First Republic was ranked No. 5 at 86.4%.

Entries to the bottom-20 valuation list were Millersburg, Pa.-based Mid Penn Bancorp Inc.; Boston-based Berkshire Hills Bancorp Inc.; Leawood, Kan.-based CrossFirst Bankshares Inc.; and Glen Head, N.Y.-based First of Long Island Corp.

Several funds initiated a position in Mid Penn in the second quarter. FJ Capital Management LLC bought a 2.11% stake, while the stakes for EJF Capital LLC, Endeavour Capital Advisors Inc. and Basswood Capital Management LLC were 1.52%, 1.13% and 0.56%, respectively.

Meanwhile, Berkshire Hills has been streamlining its business. It completed the sale of insurance assets on Sept. 1 and the sale of eight branches on Aug. 27.

The four exits from the bottom of the valuation list were West Reading, Pa.-based Customers Bancorp Inc.; Warsaw, N.Y.-based Financial Institutions Inc.; Houston-based Cadence Bancorp., which is undergoing a merger of equals with Tupelo, Miss.-based BancorpSouth Bank; and Dallas-based Texas Capital Bancshares Inc.