A vertical semiconductor device includes conductive pattern structures extending in a first direction, a trench between two adjacent conductive pattern structures in a second direction crossing the first direction, a memory layer disposed on sidewalls of the trench, first insulation layers disposed in the trench and spaced apart from each other in the first direction, channel patterns disposed on the memory layer and in the trench and spaced apart from each other in the first direction, and etch stop layer patterns disposed in the trench. Each conductive pattern structure includes conductive patterns and insulation layers alternately stacked on an upper surface of the substrate. Each etch stop layer pattern is disposed between a corresponding first insulation layer and the blocking dielectric layer. Etch stop layer patterns are spaced apart from each other in the first direction.