A CMOS semiconductor device having an n-type MOSFET and a p-type MOSFET, comprising: a gate electrode of the n-type MOSFET having a first insulation layer composed of a high-k material, and a first metal layer provided on the first insulation layer and composed of a metal material; and a gate electrode of the p-type MOSFET having a second insulation layer composed of a high-k material, and a second metal layer provided on the second insulation layer and composed of a metal material, wherein the first insulation layer and the second insulation layer are composed of the different high-k materials, and the first metal layer and the second metal layer are composed of the same metal material.