According to example embodiments of inventive concepts, a nonvolatile memory device includes a first NAND string and a second NAND string. The first NAND string include a first string selection transistor, a first ground selection transistor having a threshold voltage higher than a threshold voltage of the first string selection transistor, and first memory cells stacked on a substrate. The a second NAND string includes a second string selection transistor, a second ground selection transistor having a threshold voltage higher than a threshold voltage of the second string selection transistor, and second memory cells stacked on the substrate. A first selection line may connect the first string selection line and the first ground selection line, and a second selection line may connect the second selection line and the second ground selection line. The first and second selection lines may be electrically isolated from each other.