Tempe police spokesman Michael Pooley said Andrew Kent faces two counts of aggravated assault and two counts of endangerment.
A 17-year-old girl was burned on her legs at the Friday party and police later learned an 18-year-old ASU student was burned from the back of her shoulders to the back of her legs.
The younger teen, a student from California, was in the Valley looking at the campus when she went to the fraternity party.
According to witnesses, the teen was standing next to a type of bonfire when a male twice threw vodka on the fire.
"It just spread right to her," said one witness describing the flames.
Pooley said after the girl caught fire she was helped by others and the fraternity reportedly asked the girl to leave the party and go down the street before firefighters arrived because there was "obviously underage drinking going on."
Pooley said the injuries to the 18-year-old are less severe than the 17-year-old's.
The party was not being held on ASU property.
Kent was arrested Monday night.
As of 6 p.m. Tuesday, MCSO officials said Kent is still in custody. His bond is set at $15,000.