A method of fabricating a semiconductor device may include forming a fin structure on a substrate; forming an interface film having a first thickness on the fin structure using a first process; forming a gate dielectric film having a second thickness on the interface film using a second process different from the first process; and densifying the gate dielectric film using a third process different from the first and second processes. The second thickness may be greater than the first thickness, and the first thickness of the interface film may be unchanged after the densifying of the gate dielectric film.