A semiconductor device includes a first transistor in a first region of a substrate and a second transistor in a second region of the substrate. The first transistor includes multiple first semiconductor patterns; a first gate electrode; a first gate dielectric layer; a first source/drain region; and an inner-insulating spacer. The second transistor includes multiple second semiconductor patterns; a second gate electrode; a second gate dielectric layer; and a second source/drain region. The second gate dielectric layer extends between the second gate electrode and the second source/drain region and is in contact with the second source/drain region. The first source/drain region is not in contact with the first gate dielectric layer.