Provided are an apparatus and method for treating a substrate. More particularly, an apparatus and method for treating a substrate through a supercritical process are provided. The apparatus includes: a housing having an entrance in a predetermined surface thereof and providing a space for performing a high pressure process; a support member disposed in the housing to support a substrate; a door for opening and closing the entrance; and a pressing member configured to apply a force to the door so as to close the housing during the high pressure process.