Abstract: A semiconductor device include: a substrate; a 1st transistor formed above the substrate, the 1st transistor including a 1st channel set of a plurality of 1st nanosheet layers, a 1st gate structure surrounding the 1st nanosheet layers, and 1st and 2nd source/drain regions at both ends of the 1st channel set; and a 2nd transistor formed above the 1st transistor in a vertical direction, the 2nd transistor including a 2nd channel set of a plurality of 2nd nanosheet layers, a 2nd gate structure surrounding the 2nd nanosheet layers, and 3rd and 4th source/drain regions at both ends of the 2nd channel set, wherein the 1st channel set has a greater width than the 2nd channel set, wherein a number of the 1st nanosheet layers is smaller than a number of the 2nd nanosheet layers, and wherein a sum of effective channel widths of the 1st nanosheet layers is substantially equal to a sum of effective channel width of the 2nd nanosheet layers.