A semiconductor device includes: a substrate having an active region; a gate structure disposed in the active region; source/drain regions respectively formed within portions of the active region disposed on both sides of the gate structure; a metal silicide layer disposed on a surface of each of the source/drain regions; and contact plugs disposed on the source/drain regions and electrically connected to the source/drain regions through the metal silicide layer, respectively. The metal silicide layer is formed so as to have a monocrystalline structure.