A semiconductor device includes a substrate, a peripheral structure, a lower insulating layer, and a stack. The substrate includes a peripheral circuit region and a cell array region. The peripheral structure is on the peripheral circuit region. The lower insulating layer covers the peripheral circuit region and the cell array region and has a protruding portion protruding from a flat portion. The stack is on the lower insulating layer and the cell array region, and includes upper conductive patterns and insulating patterns which are alternately and repeatedly stacked.
