A semiconductor device includes a substrate, an interlayer insulating layer covering an upper surface of the substrate, an individual device in the interlayer insulating layer, a lower insulating layer covering a lower surface of the substrate, a through-silicon-via (TSV) structure extending through the substrate, the interlayer insulating layer and the lower insulating layer, a conductive pad connected to an upper end of the TSV structure, a via insulating layer surrounding the TSV structure, a capping insulating layer surrounding the TSV structure outside the via insulating layer. The via insulating layer and the capping insulating layer have an air gap therebetween. A portion of the air gap extends into the lower insulating layer.