A semiconductor device such as a transistor with an excellent OFF characteristic even when a channel is short is provided. A periphery of a source is surrounded by an extension region and a halo region, a periphery of a drain is surrounded by an extension region and a halo region, and a substrate with low impurity concentration is not in contact with the source or the drain. Moreover, a high-work-function electrode is provided via a gate insulator, and electrons entering the vicinity of a surface of the substrate from the extension regions are eliminated. With such a structure, the impurity concentration of the channel region can be decreased even when the channel is short, and a favorable transistor characteristic can be obtained.