The present invention is to obtain an MIS transistor which allows considerable reduction in threshold fluctuation for each transistor and has a low threshold voltage. First gate electrode material for nMIS and second gate electrode material for pMIS can be mutually converted to each other, so that a process can be simplified. Such a fact that a dependency of a work function on a doping amount is small is first disclosed, so that fluctuation in threshold voltage for each transistor hardly occurs.