A semiconductor device comprises a plurality of stack structures that include gate electrodes sequentially stacked on a substrate and are disposed along a first direction, and a plurality of separating insulation layers each of which is disposed between the stack structures. A plurality of vertical pillars penetrate each of the stack structures and are connected to the substrate. A plurality of bit lines are disposed on the vertical pillars and run across the stack structures in the first direction. A plurality of bit line contact structures connect the vertical pillars to the bit lines. A plurality of first cell dummy lines are disposed on the plurality of separating insulation layers and extend in a second direction crossing the first direction.