A semiconductor device includes a substrate, a first active pattern that includes a first side wall and a second side wall opposite to the first side wall in a second horizontal direction, a first insulating structure in a first trench extending in the first horizontal direction on the first side wall of the first active pattern, a second insulating structure in a second trench extending in the first horizontal direction on the second side of the first active pattern, and includes a first insulating layer on side walls and a bottom surface of the second trench, and a second insulating layer in the second trench on the first insulating layer, a gate-cut extending in the first horizontal direction on the first insulating structure, and a gate electrode extending in the second horizontal direction on the first active pattern.