Semiconductor devices and methods of manufacturing semiconductor devices. A semiconductor device includes a metal gate electrode stacked on a semiconductor substrate with a gate insulation layer disposed therebetween, spacer structures disposed on the semiconductor substrate at both sides of the metal gate electrode, source/drain regions formed in the semiconductor substrate at the both sides of the metal gate electrode, and an etch stop pattern including a bottom portion covering the source/drain regions and a sidewall portion extended from the bottom portion to cover a portion of sidewalls of the spacer structures, in which an upper surface of the sidewall portion of the etch stop pattern is positioned under an upper surface of the metal gate electrode.