A semiconductor device includes a pair of first and second dummy active regions extending in a first horizontal direction and spaced apart from each other in a second horizontal direction; a pair of first and second circuit active regions extending in the first horizontal direction and spaced apart in the second horizontal direction; and a plurality of line patterns extending in the second horizontal direction and spaced apart in the first horizontal direction. The pair of first and second dummy active regions may be between a pair of line patterns adjacent to each other among the plurality of line patterns. At least one of the first and second dummy active regions may have a width-changing portion in which a width of the at least one of the first and second dummy active regions changes in the second horizontal direction between the pair of line patterns adjacent to each other.