A memory device includes a substrate having an upper surface; a stacked structure disposed on the upper surface of the substrate, wherein the stacked structure includes a first insulating layer, a first conductive layer, a second insulating layer; a second conductive layer and a third insulating layer sequentially stacked on the substrate; a plurality of channel structures penetrating the stacked structure and electrically connected to the substrate, wherein each of the channel structures includes an upper portion corresponding to the second conductive layer and a lower portion corresponding to the first conductive layer; a memory layer disposed between the second conductive layer and the upper portion; and a plurality of isolation structures penetrating the stacked structure to separate the stacked structure into a plurality of sub-stacks.