A semiconductor device is provided. The semiconductor device includes a substrate including a first region and a second region, a first gate structure extending in a first direction on the first region of the substrate, the first gate structure including a first gate insulation film and a first work function film disposed on the first gate insulation film, and a second gate structure extending in the first direction on the second region of the substrate, the second gate structure including a second gate insulation film and a second work function film disposed on the second gate insulation film, wherein a first thickness of the first work function film in a second direction intersecting the first direction is different from a second thickness of the second work function film in the second direction, and wherein a first height of the first work function film in a third direction perpendicular to the first and second directions is different from a second height of the second work function film in the third direction.