A semiconductor device includes a first insulating interlayer on a first region of a substrate and a second insulating interlayer on a second region of the substrate, a plurality of first wiring structures on the first insulating interlayer, the first wiring structures being spaced apart from each other, a plurality of second wiring structures filling a plurality of trenches on the second insulating interlayer, respectively, an insulation capping structure selectively on a surface of the first insulating interlayer between the first wiring structures and on a sidewall and an upper surface of each of the first wiring structures, the insulation capping structure including an insulating material, a third insulating interlayer on the first and second wiring structures, and an air gap among the first wiring structures under the third insulating interlayer.