Firefighters were called to West San Carlos St. near Sunol Street at 2:23 a.m.
San Jose Fire Battalion Chief Dave Ennes determined it was too dangerous to send firefighters into the building. "When I pulled up there was probably 30 foot flames. It was called a defensive fire right away. We're not going to commit our people to a building like this that's already had fires in it. That's why we went defensive with the large caliber lines," said Ennes.
Firefighters called for two-alarms to help keep the flames from spreading to a big apartment complex still under construction next door.
Firefighters say they've responded to at least one fire at this vacant building before. They say homeless have been known to stay in this building.
Fire cause investigators are expected to take a closer look at what started the fire.
W. San Carlos St. was blocked off for a few hours, but is now back open.