A semiconductor device includes first and second active patterns disposed on a substrate, a field insulating film disposed between the first and second active patterns, a first gate structure intersecting the first active pattern, and a second gate structure intersecting the second active pattern, in which the first gate structure includes a first gate insulating film on the first active pattern, a first upper insertion film on the first gate insulating film, and a first upper conductive film on the first upper insertion film, and the second gate structure includes a second gate insulating film on the second active pattern, a second upper insertion film on the second gate insulating film, and a second upper conductive film on the second upper insertion film. Each of the first and second upper insertion films may include an aluminum nitride film. Each of the first and second upper conductive films may include aluminum.