A semiconductor device includes first to sixth active patterns extending in a first direction and spaced apart in the first direction and a second direction; a field insulating layer between the first and second active patterns, an upper surface thereof being lower than upper surfaces of the first and second active patterns; a first gate structure on the field insulating layer and the first active pattern and extending in the second direction; a second gate structure on the field insulating layer and the second active pattern and extending in the second direction; a first separation trench extending between the second and third active patterns and the fifth and sixth active patterns, and a second separation trench extending between the first and second gate structures, wherein a lowest surface of the first separation trench is higher than a lowest surface of the second separation trench.