A semiconductor device includes a semiconductor substrate, a device region including first and second parts, first and second gate electrodes formed in the first and the second parts, first and second source regions, first and second drain regions, first, second, third, and fourth embedded isolation film regions formed under the first source, the first drain, the second source, and the second drain regions, respectively. Further, the first drain region and the second source region form a single diffusion region, the second and the third embedded isolation film regions form a single embedded isolation film region, an opening is formed in a part of the single diffusion region so as to extend to the second and the third embedded isolation film regions, and the opening is filled with an isolation film.