A two-alarm blaze was reported at about 1:50 a.m. at an apartment building at 639 Caliente Drive, fire Capt. Dave Pitts said.
The fire was controlled at about 4:30 a.m.
The second-story apartment where the fire is believed to have started was "completely gutted," Pitts said. Two other units sustained fire damage, and additional apartments sustained smoke and water damage, he said.
A male occupant suffered burns and was transported to Santa Clara Valley Medical Center. His injuries are not life-threatening, Pitts said.
The American Red Cross responded to assist about 40 people who were displaced, most of them only temporarily, Pitts said.
The Santa Clara, Mountain View, and Palo Alto fire departments also assisted.
The cause of the fire is under investigation.