A semiconductor device in which misalignment does not cause short-circuiting and inter-wiring capacitance is decreased. Plural wirings are provided in a first interlayer insulating layer. An air gap is made between at least one pair of wirings in the layer. A second interlayer insulating layer lies over the wirings and first interlayer insulating layer. The first bottom face of the second interlayer insulating layer is exposed to the air gap. When a pair of adjacent wirings whose distance is shortest are first wirings, the upper ends of the first interlayer insulating layer between the first wirings are in contact with the first wirings' side faces. The first bottom face is below the first wirings' upper faces. b/a≦0.5 holds where a represents the distance between the first wirings and b represents the width of the portion of the first interlayer insulating layer in contact with the first bottom face.