A method of fabricating a semiconductor device includes forming a dummy gate on a substrate, forming a dummy gate mask on the dummy gate, forming a gate spacer on the substrate, the gate spacer covering at least one sidewall surface of the dummy gate and the dummy gate mask, forming a recess on at least one side of the dummy gate by etching the substrate, and forming an epitaxial layer in the recess using an epitaxial growth process. The forming of the dummy gate mask includes forming an oxide layer and a dummy gate mask layer on the dummy gate.