A metal oxide Semiconductor (MOS) transistor includes a gate insulating film disposed on a surface of a silicon substrate. The gate insulating film has a central portion formed on the silicon substrate and comprising a nitride insulating film, and an end portion located on each side of the central portion, the end portion being thicker than the central portion and formed of an oxide insulating film. The MOS transistor also includes a p-type gate electrode formed on the gate insulating film, sidewalls formed on both sides of the gate insulating film and the gate electrode, a pair of p-type source/drain areas formed in surface portions of the silicon substrate, and a channel area located between the pair of source/drain areas.