A semiconductor device includes: an isolation region formed in a semiconductor substrate; an active region surrounded by the isolation region of the semiconductor substrate; a fully silicided first gate line formed on the active region; a fully silicided second gate line formed on the isolation region; a first sidewall formed on a side of the first gate line; a second sidewall formed on a side of the second gate line. The length between the top and bottom surfaces of the first sidewall is different from that between the top and bottom surfaces of the second sidewall.