Semiconductor device and method of manufacturing the same

A semiconductor device comprising:

• an SOI (Silicon On Insulator) substrate including a semiconductor substrate, an insulating film on the semiconductor substrate, and a semiconductor layer on the insulating film;
• a first field-effect transistor including a well formed in the semiconductor substrate, a first gate electrode formed on the semiconductor layer via a gate insulating film, and a source/drain region formed in the semiconductor layer beside the first gate electrode and also formed in an epitaxial layer in contact with an upper surface of the semiconductor layer beside the first gate electrode;
• an isolation region formed by burying a film in a trench of the SOI substrate, which is comprised of the semiconductor layer, the insulating film and the semiconductor substrate;
• and
• a contact plug connected to the epitaxial layer,
• wherein, in cross-section view, a concaved portion is formed at a portion of an upper surface of the isolation region, which is located beside a sidewall of the semiconductor layer,
• wherein, in cross-section view, a bottom portion of the concaved portion is located lower than the upper surface of the semiconductor layer,
• wherein an inside of the concaved portion is embedded with the epitaxial layer,
• wherein the sidewall of the semiconductor layer is covered with the epitaxial layer, and
• wherein an electric potential supplied to the well and an electric potential supplied to the source/drain region through the contact plug are controlled separately from each other.