A semiconductor device includes a substrate; a device area of the substrate, the device area including a plurality of device unit cells; and a dummy cell array arranged around the device area. The dummy cell array includes a plurality of dummy unit cells repeatedly arranged in a first direction and a second direction perpendicular to the first direction, each of the dummy cell unit having a structure corresponding to a device unit cell. The device unit cell includes at least a first transistor in the device area. The structure of the dummy unit cell includes an active area and a gate line. For each dummy unit cell, the active area and the gate line extend beyond a cell boundary that defines the dummy unit cell.