A vertical type semiconductor device includes insulation patterns on a substrate and spaced apart from each other in a first direction perpendicular to a top surface of the substrate, a channel structure on the substrate and penetrating through the insulation patterns, a first conductive pattern partially filling a gap between the insulation patterns adjacent to each other in the first direction and the channel structure and having a slit in a surface thereof, the slit extending in a direction parallel with the top surface of the substrate, and a second conductive pattern on the first conductive pattern in the gap and filling the slit.