Provided are a semiconductor device and a method of fabricating a semiconductor device. The semiconductor device includes a first active fin and a second active fin which protrude from a substrate and extend along a first direction, a first gate structure which is on the first active fin to extend along a second direction intersecting the first direction, a second gate structure which is located adjacent to the first gate structure in the second direction and is on the second active fin to extend along the second direction, and a dummy structure which is in a space between the first gate structure and the second gate structure.