stack structures spaced apart from each other on a semiconductor substrate, wherein each of the stack structures comprises interlayer insulating layers and semiconductor patterns alternately stacked on the semiconductor substrate;

conductive patterns provided between the interlayer insulating layers vertically adjacent to each other and connected to the semiconductor patterns; and

a protective structure covering a top surface of the semiconductor substrate between the stack structures,

wherein a top surface of the protective structure is located between a top surface and a bottom surface of a lowermost interlayer insulating layer of the interlayer insulating layers,

wherein the protective structure covers a sidewall of the lowermost interlayer insulating layer.