A semiconductor device includes an active fin on a substrate, a device isolation film covering a lower portion of the active fin, a gate structure covering the active fin and the device isolation film, and a gate spacer on a side wall of the gate structure, wherein a side wall of the gate structure disposed on the device isolation film is inclined at a uniform inclination from a point higher than a half of a height of the gate structure to a bottom of the gate structure, and an inner side wall of the gate spacer on the device isolation film is inclined at a uniform inclination from a point higher than a half of a height of the gate spacer to a bottom of the gate spacer while forming an acute angle with a bottom surface of the gate spacer.