The fire was reported shortly before 5:30 a.m. at 37149 Dondero Way and spread to the house next door at 37141 Dondero Way, Fremont fire Battalion Chief Jim Martin said.
Firefighters responded and extinguished the blaze in about 45 minutes, Martin said.
A firefighter who was on the roof of one of the homes fell partially through the roof and suffered burns and blisters to his hand, according to Martin. The firefighter was treated and released at the scene, he said.
No other injuries were reported in the fire, which displaced a total of 10 people and two dogs from the two homes, Martin said.
Investigators were at the scene of the blaze Monday morning to try to determine what sparked the fire, Martin said.