A semiconductor device includes a substrate, a first gate structure and a second gate structure on the substrate, a single back gate structure between the first gate structure and the second gate structure, a first structure including a first vertical channel region extending in a vertical direction, at least a portion of the first vertical channel region between the first gate structure and the single back gate structure, and a second structure including a second vertical channel region extending in the vertical direction. The second structure is spaced apart from the first structure, and at least a portion of the second vertical channel region is between the second gate structure and the single back gate structure.