The blaze was reported at 7:42 a.m. at a two-story fourplex at 5563 Harlow Way, near Blossom Hill Road, fire Capt. Chuck Rangel said.
Firefighters arrived and had the fire controlled by 8:15 a.m.
Flames were confined to a downstairs unit but the smoke spread upstairs, Rangel said.
The fire caused "significant damage to the kitchen and eating area" in the downstairs unit, he said.
Four people were displaced, but no residents were injured, Rangel said.
However, a small dog was found dead inside the building, he said. A second dog survived the blaze.
The cause of the fire remains under investigation.