Disclosed are semiconductor devices and methods of fabricating the same. The semiconductor device includes a plurality of gate structures that are spaced apart from each other in a first direction on a substrate and extend in a second direction intersecting the first direction, and a plurality of separation patterns penetrating immediately neighboring ones of the plurality of gate structures, respectively. Each of the plurality of separation patterns separates a corresponding one of the neighboring gate structures into a pair of gate structures that are spaced apart from each other in the second direction. The plurality of separation patterns are spaced apart from and aligned with each other along the first direction.