A semiconductor device includes a semiconductor substrate having a first area and a second area, and a first gate pattern on the first area and a second gate pattern on the second area. The first gate pattern includes a first gate insulating pattern on the first area, a first gate barrier pattern on the first gate insulating pattern, and a first work function metal pattern on the first gate barrier pattern. The second gate pattern includes a second gate insulating pattern on the second area, a second gate barrier pattern on the second gate insulating pattern, and a second work function metal pattern on the second gate barrier pattern. The first gate barrier pattern includes a metal material different than the second gate barrier pattern.