Surveillance cameras captured images of the suspect during the two Campbell robberies, which occurred at a Guaranty Bank on Oct. 31 and a Washington Mutual Bank on Monday.
The man is also suspected of robbing a Washington Mutual Bank in Pleasanton on Oct. 30, police said.
During the robberies, the man wore a white dress shirt and a blue jacket with red lining. He gave the tellers a demand letter stating he had a gun, and fled with the money, police said.
Witnesses told police he has a European accent. After Monday's robbery, witnesses reported seeing him run toward a white van parked nearby.
Anyone with information is asked to call Campbell Police Investigator Tom Rogers at (408) 866-2179.