A semiconductor device includes a first and second active regions extending in a first direction and having respective first and second widths in a second direction, the second width greater than the first width, a connection region connected to the first and second active regions and having a third width, between the first and second widths in the second direction, first and second gate structures respectively intersecting the first and second active regions and extending in the second direction, and a dummy structure intersecting at least a portion of the connection region, extending in the second direction, and between the first and second gate structures in the first direction. The dummy structure includes first and second pattern portions spaced apart from a side surface of the first gate structure by respective first and second distances in the first direction, the second distance greater than the first distance.