A semiconductor device includes a substrate, a fin active region pattern on the substrate, the fin active region pattern including an upper region and a lower region, a device isolation layer pattern surrounding the fin active region pattern, a gate pattern on the upper region of the fin active region pattern, and a stressor on the lower region of the fin active region pattern, wherein a top surface of the device isolation layer pattern is lower than a top surface of the upper region and higher than a top surface of the lower region.