A p type group III nitride semiconductor layer can be manufactured without causing its crystal deterioration, and without requiring any complicated post-treatment, by repeating a plurality of times the following steps: the step A of growing a group III nitride semiconductor layer containing p type impurities; the step B of discontinuing the growth of the group III nitride semiconductor layer by stopping supplies of the respective material gases and the carrier gas, and replacing an atmospheric gas within a film forming apparatus with an inert gas, and reducing a temperature of the substrate from a growth temperature; and the step C of resuming the growth of the group III nitride semiconductor layer by again raising the temperature of the substrate and supplying the material gases and the carrier gas into the film forming apparatus. Thereby, the activation of the semiconductor layer is attainable by releasing hydrogen incorporated into the semiconductor layer, and reducing thermal damage, resulting in suppressing the crystal deterioration.