A Group III-V compound semiconductor includes, at least, a substrate, a buffer layer of the general formula InuGavAlwN (wherein, 0≦u≦1, 0≦v≦1, 0≦w≦1, u+v+w=1) and a Group III-V compound semiconductor crystal layer of the general formula InxGayAlzN (wherein, 0≦x≦1, 0≦y≦1, 0≦z≦1, x+y+z=1), in this order, wherein the buffer layer has a thickness of at least about 5 Å and not more than about 90 Å. A method is provided for producing the Group III-V compound semiconductor, including forming a buffer layer of the general formula InuGavAlwN on a substrate to give a thickness of at least about 5 Å and not more than about 90 Å at temperatures lower than the growing temperature of the compound semiconductor crystal layer before growing the compound semiconductor crystal layer, and then growing a Group III-V compound semiconductor crystal layer of the general formula InxGayAlzN on the buffer layer.