A mother, her three children and one of their friends were in the home when the fire was reported about 4:30 a.m., said Fire Marshal Jason Napier.
The fire started in an upstairs bedroom where a teenage boy was awakened by burns, Napier said. He alerted the house, ran downstairs and got his mother who called 911. They tried to put out the fire with water from the kitchen but had to flee.
A brother and his friend were in another upstairs bedroom, Napier said. The brother went out the window, but his friend did not make it out and could not be reached through a hall because of heat and smoke. His body was found by firefighters.
"He tried to get his buddy out with him," Napier said. "For some reason he was disoriented and couldn't make it out."
The mother and another child downstairs escaped uninjured.
The boy with burns and the brother who was injured jumping out the window were taken to St. Joseph Medical Center.
Names are not being released, Napier said.
There were no smoke alarms in the home, and an earlier alert probably would have saved a life, Napier said.
The house was fully involved in flames when firefighters arrived. Investigators are trying to determine exactly how the fire started.
The previous fatal fire in Bellingham was last April when a woman and her brother were killed by a blaze in their home.