A semiconductor device may include a cell gate conductive pattern in a cell array area that extends to a step area, a cell vertical structure in the cell array area that extends through the cell gate conductive pattern, a cell gate contact structure on the cell gate conductive pattern in the step area, a cell gate contact region in the cell gate conductive pattern and aligned with the cell gate contact structure, a first peripheral contact structure spaced apart from the cell gate conductive pattern, a second peripheral contact structure spaced apart from the first peripheral contact structure, a first peripheral contact region under the first peripheral contact structure, and a second peripheral contact region under the second peripheral contact structure. The cell gate contact region may include a first element and a remainder of the cell gate conductive pattern may not substantially include the first element.