A semiconductor device includes a first transistor, a division pattern, and a second transistor sequentially stacked on a substrate. The first transistor includes a first gate structure, a first source/drain layer at each of opposite sides of the first gate structure, and first semiconductor patterns spaced apart from each other in a vertical direction. Each of the first semiconductor patterns extends through the first gate structure and contacts the first source/drain layer. The division pattern includes an insulating material. The second transistor includes a second gate structure, a second source/drain layer at each of opposite sides of the second gate structure, and second semiconductor patterns spaced apart from each other in the vertical direction. Each of the second semiconductor patterns extends through the second gate structure and contacts the second source/drain layer. The first source/drain layer does not directly contact the second source/drain layer.