A method of manufacturing a memory device includes: providing a substrate; forming in a cell region a channel extending in a direction perpendicular to an upper surface of the substrate and a plurality of gate electrode layers and a plurality of insulating layers stacked alternatingly on the substrate to be adjacent to the channel; forming a plurality of circuit elements on the substrate at a peripheral circuit region disposed at a periphery of the cell region; and forming an interlayer insulating layer on the substrate in the cell region and the peripheral circuit region, the interlayer insulating layer including a first, bottom interlayer insulating layer covering the plurality of circuit elements and at least a portion of the plurality of gate electrode layers, and a second, top interlayer insulating layer disposed on the first interlayer insulating layer.