Signature Bank said it would offer at least 4.1 million shares of common stock, which would raise its number outstanding by 9.9%.
With the offering, the New York regional bank joins a growing list of companies that have been turning to improving equity markets to raise capital.
Signature, which has 24 offices throughout the New York metropolitan area, is known as one of the country's stronger regionals. It quickly repaid $120 million it received from the Troubled Asset Relief Program, and it posted a record high income in its first-quarter results. It had about 41.4 million shares outstanding as of the end of March.
Shares fell 4.3% in after-hours trading, to $56.88, on the offering's dilutive effect on share value, although they later recovered to $58.05.
Through the close, the stock had risen 17% so far this year, better than the wider market.