A semiconductor device may include stacks extended in a first direction on a substrate, separation structures extended in the first direction and respectively provided between the stacks, vertical channels penetrating each of the stacks, bit lines extended in a second direction crossing the first direction, each of the vertical channels being overlapped with a pair of the bit lines, and contact plugs connecting the bit lines to the vertical channels. Each of the stacks may include electrodes stacked on the substrate and at least two upper separation patterns dividing an upper one of the electrodes into several portions in the second direction. The vertical channels may be classified into a plurality of types, depending on a distance from one of the separation structures in the second direction, and each of the bit lines may be connected to all types of the vertical channels.