A semiconductor device is provided. A semiconductor device includes a filler cell including first and second insulating structures, the first and second insulating structures extending in a first direction, the filler cell being defined by first cell boundaries; and a neighboring cell including a third insulating structure, the third insulating structure extending in the first direction, the neighboring cell being adjacent to the filler cell in the first direction and defined by second cell boundaries, wherein the first and second insulating structures are spaced apart from one another in a second direction, is the second direction being perpendicular to the first direction.