A semiconductor device includes a peripheral circuit area disposed on a first substrate and including circuit devices. A memory cell area is disposed on a second substrate and includes memory cells. A through wiring area includes a through contact plug and an insulating area. The through contact plug extends through the memory cell area and the second substrate and connects the memory cell area to the circuit devices. The insulating area surrounds the through contact plug. The insulating area includes a first insulating layer penetrating through the second substrate, a plurality of second insulating layers, a third insulating layer having a vertical extension portion, and a plurality of horizontal extension portions extended in parallel to a top surface of the second substrate from a side surface of the vertical extension portion to contact the second insulating layers.