Provided are semiconductor devices having various line widths and a method of manufacturing the semiconductor device. The semiconductor device includes: a substrate including a first region and a second region, a plurality of first gate lines extending in a first direction in the first region and each having a first width in a second; a plurality of second gate lines extending in the first direction in the second region and each having a second width that is different from the first width in the second direction and a pitch that is the same as a pitch of the plurality of first gate lines; a spacer layer covering opposite side walls of each of the plurality of first gate lines and each of the plurality of second gate lines; and a first base layer arranged between the substrate and the spacer layer in the first region.