A semiconductor integrated circuit is provided in which a CMOS transistor is formed on a first conductivity type semiconductor film provided on a first conductivity type supporting substrate through an embedded insulating film. Second conductivity type source and drain regions are formed in the semiconductor film. The source region has an ultra-shallow high-density second conductivity type source extension region at a boundary with a channel region, a low-density second conductivity type source extension region under the ultra-shallow high-density second conductivity type source extension region, and a high-density second conductivity type source extension region under the low-density second conductivity type source extension region. The drain region has an ultra-shallow high-density second conductivity type drain extension region at a boundary with the channel region, a low-density second conductivity type drain extension region under the ultra-shallow high-density second conductivity type drain extension region, and a high-density second conductivity type drain extension region under the low-density second conductivity type drain extension region. A gate insulating film is formed on an upper surface of the semiconductor film. A gate electrode is formed on an upper surface of the gate insulating film.