To obtain a group III nitride semiconductor enhancing characteristics such as performance characteristics, reliability, productivity, availability and the like and a semiconductor device.

A p-type group III nitride semiconductor comprises a low- temperature GaN buffer layer 11 and a p-type GaN layer 12 sequentially laminated on a sapphire board 10. This layer 12 contains In as the group III element impurity of 0.1%. As a p-type dopant, Mg of 6×1019 cm-3 is contained. The layer 12 exhibits a p-type of low resistance of carrier concentration of 8×1017 cm-3. If the In is not contained, the carrier concentration is 1×1017 cm-3. At least as the p-type impurity, one or more elements are doped. The p-type group III nitride semiconductor made of a compound of any or more of Ga, Al, In and B and the nitrogen contains, except the constituting element, one or more group III elements selected from Ga, Al, In and B and a fine amount of the impurity and is a semiconductor of low resistance having excellent electric characteristics for increasing the carrier concentration as compared with the conventional group III nitride semiconductor containing no group III element impurity.