A semiconductor device may include gate structures spaced apart above a top surface of a substrate. The gate structures may include a horizontal electrode extending in a first direction parallel with the top surface of a substrate. An isolation insulating layer may be disposed between the gate structures. A plurality of cell pillars may penetrate the horizontal electrode and connect to the substrate. The plurality of cell pillars may include a minimum spacing defined by a shortest distance between any two of the plurality of cell pillars. The thickness of the horizontal electrode may be greater than the minimum spacing of the cell pillars.