A semiconductor device includes a substrate having cell array and extension regions, a gate electrode structure having gate electrodes stacked in a first direction, a channel through the gate electrode structure on the cell array region, a first division pattern extending in the second direction on the cell array and extension regions, the first division pattern being at opposite sides of the gate electrode structure in a third direction, an insulation pattern structure partially through the gate electrode structure on the extension region, a through via through the insulation pattern structure, and a support layer on the gate electrode structure and extending on the cell array and extension regions, the support layer contacting an upper sidewall of the first division pattern, and the support layer not contacting an upper surface of a portion of the first division pattern on the extension region adjacent to the insulation pattern structure.