The report of a fire at 1624 Dell Ave. came in at 4:53 p.m., Battalion Chief Ron Vega said.
Arriving crews found the back of the building in flames, which had burned through the roof.
A third alarm was called, with a total of 60 firefighters responding, including crews from the San Jose Fire Department, Vega said.
The fire was put out after a few hours, Vega said. Crews remained at the site to monitor the building around 11 a.m.
No injuries were reported at the unoccupied building, he said.
Vega said the cause of the fire is under investigation.
The back business was destroyed, while the rest of the building sustained water damage, he said.
McCalmont Engineering, a solar power company, is listed at the address of the fire.
A few hours after responding to the Dell Avenue fire, Vega said the sprinklers went off at the Courtyard Marriott hotel, located at 655 Creekside Way in Campbell.
Further details about what triggered the sprinklers to go off were not immediately available.