Three-dimensional (3D) semiconductor devices may be provided. A 3D semiconductor device may include a substrate including a chip region and a scribe line region, a cell array structure including memory cells three-dimensionally arranged on the chip region of the substrate, a stack structure disposed on the scribe line region of the substrate and including first layers and second layers that are vertically and alternately stacked, and a plurality of vertical structures extending along a vertical direction that is perpendicular to a top surface of the substrate and penetrating the stack structure.