A semiconductor device includes: a substrate; an active pattern provided on the substrate and extending in a first horizontal direction; a plurality of nanosheets spaced apart from each other in a vertical direction and stacked on the active pattern; a gate electrode provided on the active pattern and extending in a second horizontal direction different from the first horizontal direction, the gate electrode surrounding each of the plurality of nanosheets; a source/drain region provided on the active pattern at two sides of the gate electrode; a first inner spacer provided between the gate electrode and the source/drain region and between adjacent nanosheets of the plurality of nanosheets, the first inner spacer being spaced apart from the plurality of nanosheets in the vertical direction; and a first barrier layer provided on a first side of the gate electrode and between the first inner spacer and one of the plurality of nanosheets.