The first in the string of five robberies occurred at about 5 p.m. on Jan. 18 at a U.S. Bank at 10381 S. DeAnza Blvd. in Cupertino.
It was followed by a robbery at 2:20 p.m. on Jan. 24 at a Wells Fargo branch at 6465 Almaden Expressway in San Jose.
The three other robberies occurred this month. One was at about 2:30 p.m. on Feb. 1 at a Bank of the West at 18860 Cox Ave. in Saratoga; another happened at roughly 2:15 p.m. on Feb. 6 at the Wells Fargo at 23000 Homestead Road in Cupertino; and the most recent was on Tuesday, shortly before 3 p.m., at another Wells Fargo at 2792 Homestead Road in Santa Clara.
Wells Fargo is offering the reward money for the arrest of the suspect, who is believed to be responsible for all five robberies.
Various law enforcement agencies are investigating the heists, including the sheriff's office and the San Jose and Santa Clara police departments.
The suspect is described as a white man about 35 years old, standing between 5 feet 6 inches and 6 feet tall, with a muscular build.
Authorities have released images taken from surveillance footage of the suspect.
In each incident, the suspect entered the bank, presented a note to a teller demanding money and fled with cash.
Anyone with information on the investigation is asked to call Santa Clara County sheriff's Detective Sgt. Paula McAllister at (408) 808-4500, San Jose police Detective Ryan Chan at (408) 277-4166, or Santa Clara police Detective Sgt. Hoesing at (408) 615-4814.