The suspect was armed with a dark-colored semi-automatic pistol and took an undisclosed amount of cash in all three robberies.
The first armed robbery occurred at Willow Market at 37 Willow St. at 7:43 p.m. Tuesday, sheriff's officials said.
The next armed robbery occurred the following day at Panaderia Michoacan Market at 2561 El Camino Real at 3:34 p.m.
The third armed robbery occurred Thursday at 1:03 p.m. at El Paisano Carniceria Market at 2856 Middlefield Road, according to the sheriff's office.
The suspect is described as a Hispanic man in his 20s or 30s, standing 5 feet 10 inches tall, with a thin build and short dark hair.
Anyone who may have witnessed the robberies or has information about the suspect is asked to contact Detective Andy Armando at (650) 363-4347 or via email at aarmandosmcgov.org. People wishing to remain anonymous can call (800) 547-2700.