A semiconductor device includes a substrate having first and second active regions. A first active pattern is on the first active region and includes first source/drain patterns and a first channel pattern therebetween. A second active pattern is on the second active region and includes second source/drain patterns and a second channel pattern therebetween. A gate electrode includes a first gate electrode on the first channel pattern and a second gate electrode on the second channel pattern. A gate cutting pattern is between the first and second gate electrodes and separates the first and second gate electrodes from each other. A pair of gate spacers is on opposite sidewalls of the first gate electrode extending along opposite sidewalls of the gate cutting pattern towards the second gate electrode. The gate cutting pattern includes first to third parts having maximum widths that increase from the first to the third part.