A semiconductor device includes: a semiconductor substrate; a gate electrode formed on the semiconductor substrate with a gate insulating film interposed therebetween; a side wall spacer formed on a side wall of the gate electrode; source/drain regions formed in opposing portions of the semiconductor substrate with the gate electrode and the side wall spacer interposed therebetween; and a stress-applying insulating film covering the gate electrode, the side wall spacer, and an upper surface of the semiconductor substrate. A gate-length-direction thickness of an upper portion of the side wall spacer is at least larger than a gate-length-direction thickness of a middle portion thereof.