A semiconductor device includes a first source/drain structure having a first length in a horizontal direction, as viewed in a planar cross-sectional view, the horizontal direction being perpendicular to a vertical direction, a second source/drain structure having a second length in the horizontal direction, as viewed in the planar cross-sectional view, the second length being less than the first length, channels extending between the first source/drain structure and the second source/drain structure, the channels being spaced apart from each other in the vertical direction, at least one sacrificial pattern between adjacent ones of the channels, and a trench penetrating the channels and the at least one sacrificial pattern.