A semiconductor device includes a substrate including first and second regions; a first active pattern including a first lower pattern and first sheet patterns; a second active pattern including a second lower pattern, a height of the second lower pattern being identical to a height of the first lower pattern, and second sheet patterns; a first gate structure including a first gate insulating film and a first gate electrode; a second gate structure including a second gate insulating film, and a second gate electrode, a width of the second gate electrode being greater than a width of the first gate electrode; a first source/drain pattern on the first lower pattern and connected to the first sheet patterns; and a second source/drain pattern on the second lower pattern and connected to the second sheet patterns, wherein a number of first sheet patterns is smaller than a number of second sheet patterns.