The teen and his siblings, ages 8, 10 and 12, were at home alone when a woman rang the doorbell Friday afternoon, Phoenix police Officer James Holmes said.
The teen didn't open the door because he didn't recognize the woman.
Soon after, the teen heard a loud bang on the door, rushed his siblings upstairs and got a handgun from his parent's bedroom.
When he got to the top of the stairs, he saw a man break through the front door and point a gun at him.
The boy shot the 37-year-old man, who was taken to a hospital in extremely critical condition and underwent surgery. The man was upgraded to critical condition and is expected to survive and be booked into jail within the week on counts of aggravated assault and burglary, Holmes said.
"The police and indeed our community does not ever want to see a situation where a teenager of that age has to take a weapon to protect his family … but this young man did exactly what he should have done," he said. "I'm not sure he gave full thought about what he had to do. He just acted."