A semiconductor device includes an active pattern on a substrate, source/drain patterns on the active pattern, channel patterns on the active pattern and connected to the source/drain patterns each including stacked semiconductor patterns, gate electrodes on the channel patterns and extending in parallel to each other in a first direction, and a power line adjacent to the active pattern. The power line extends in a second direction. The active pattern includes a first region having a first width, a second region having a second width, and a third region between the first and second regions. The first region has a first sidewall extending in the second direction. The second region has a second sidewall extending in the second direction. The third region has a recessed sidewall that connects the first and second sidewalls. The recessed sidewall is recessed toward the power line.