A method of fabricating a semiconductor device includes providing a dummy gate insulation film formed on a substrate, the dummy gate insulation film including a first material and providing a spacer formed at least one side of the gate insulation film, the spacer including the first material, removing the first material included in the dummy gate insulation film by a first process, removing the dummy gate insulation film from which the first material has been removed by a second process different from the first process, and sequentially forming a gate insulation film and a gate electrode structure on the substrate.