Police noticed smoke flowing from a vacant home in North Philadelphia around 3 a.m., WPVI-TV reported. When firefighters arrived, they found the rowhouse next door in flames.
Curt Singleton, 26, was found downstairs. His fiancee Nyasha Vicks, 25, and their 6-month-old daughter, Pahyje Singleton, were upstairs.
The victims were rushed to Temple University Hospital, where they were pronounced dead.
Fire Commissioner Lloyd Ayers said the fire appeared to have begun in the kitchen.
"When he [a fireman] pulled the gentleman out the door, the gentleman was on fire," said neighbor Peaches McLeod.
Two other homes with six residents were evacuated because of smoke and water damage.
The home had two smoke detectors, but one had no batteries and the other a dead battery.