A vertical-type semiconductor device includes a semiconductor substrate having a cell region and a peripheral circuit region, a wordline structure on the cell region of the semiconductor substrate, the wordline structure including a plurality of wordlines stacked on top of each other, a semiconductor structure through the wordline structure, a gate dielectric between the wordline structure and the semiconductor structure, and a dummy wordline structure on the peripheral circuit region, the dummy wordline structure having a vertical structure and including same components as the wordline structure.