CHICAGO — Fifth Third Bancorp will buy Chicago-based MB Financial Bank for $4.7 billion, the banks announced Monday.

The merger will create the fourth-largest Chicago bank in total deposits with a 6.5 percent market share, and give the combined company 20 percent of the city’s “middle market” banking relationships. MB branches will take the Fifth Third Bank name.

“We view MB Financial as a unique partner in our efforts to build scale in this strategically important market,” Greg Carmichael, president and CEO of Fifth Third, said in a news release.

There will be 239 Chicago-area branches with $25.4 billion in combined deposits, Fifth Third spokesman Andrew Hayes said. This will rank the bank fourth in total deposits and second in retail deposits in the Chicago market.

The transaction is 90 percent stock, with the balance to be paid in cash. Shareholders of MB Financial will receive $54.20 a share in total consideration, consisting of 1.45 shares of Fifth Third stock and $5.54 in cash for each share of MB Financial stock. That represents a premium of about 24 percent over MB Financial’s closing price of $43.65 a share on Friday.

MB Financial’s president and CEO, Mitch Feiger, was named CEO of the Chicago region for the combined bank. “Our commercial expertise and strong credit culture complement the strengths of Fifth Third in large corporate lending, capital markets, wealth management and the payments business,” Feiger said in the news release.

Two members of MB Financial’s board are expected to join Fifth Third’s board, the companies said.

A closing date has not been determined, and the deal will require regulatory and shareholder approval.

A century-old Chicago bank with a focus on middle-market business customers, MB Financial has about $20 billion in assets.

Cincinnati-based Fifth Third entered the Chicago market with the 2000 acquisition of Old Kent Financial.