A semiconductor device includes an NMOS transistor and a PMOS transistor. The NMOS transistor includes a channel area formed in a silicon substrate, a gate electrode formed on a gate insulating film in correspondence with the channel area, and a source area and a drain area formed in the silicon substrate having the channel area situated therebetween. The PMOS transistor includes another channel area formed in the silicon substrate, another gate electrode formed on another gate insulating film in correspondence with the other channel area, and another source area and another drain area formed in the silicon substrate having the other channel area situated therebetween. The gate electrode has first sidewall insulating films. The other gate electrode has second sidewall insulating films. The distance between the second sidewall insulating films and the silicon substrate is greater than the distance between the first sidewall insulating films and the silicon substrate.