A semiconductor device has an n-channel MISFET having first diffusion layers formed in a first region of a surface portion of a semiconductor substrate so as to sandwich a first channel region therebetween, a first gate insulating film formed on the first channel region, and a first gate electrode including a first metal layer formed on the first gate insulating film, and a first n-type polysilicon film formed on the first metal layer, and a p-channel MISFET having second diffusion layers containing boron as a dopant and formed in a second region of the surface portion of the semiconductor substrate so as to sandwich a second channel region therebetween, a second gate insulating film formed on the second channel region, and a second gate electrode including a second metal layer containing nitrogen or carbon and formed on the second gate insulating film and a second n-type polysilicon film formed on the second metal layer and having a boron concentration of not more than 5×1019 cm−3 in a portion adjacent an interface with the second metal layer.