A semiconductor device including a substrate that includes first to third regions; a first channel structure on the first region and including first channel patterns that are vertically stacked on the substrate; a second channel structure on the second region and including a second channel pattern on the substrate; a third channel structure on the third region and including third channel patterns and fourth channel patterns that are vertically and alternately stacked on the substrate; first to third gate electrodes on the first to third channel structures; and first to third source/drain patterns on opposite sides of the first to third channel structures, wherein the first, second, and fourth channel patterns include a first semiconductor material, and the third channel patterns include a second semiconductor material different from the first semiconductor material.