A semiconductor device includes a lower structure, a plurality of conductive wirings on the lower structure, an interlayer insulating layer on the lower structure and on side surfaces of the plurality of conductive wirings, a protective insulating layer on the interlayer insulating layer and the plurality of conductive wirings, and an upper insulating structure. The upper insulating structure includes an upper interlayer portion on the protective insulating layer, and a first extension portion extending from the upper interlayer portion, penetrating through the protective insulating layer, the interlayer insulating layer, and a first conductive wiring among the plurality of conductive wirings, and extending into the lower structure.