A manufacturing method of a nitride semiconductor device includes: introducing a p type impurity into at least a part of an upper layer portion of a first nitride semiconductor layer to form a p type impurity introduction region; forming a second nitride semiconductor layer from an upper surface of the first nitride semiconductor layer so as to include the p type impurity introduction region; and performing an anneal treatment in a state where the second nitride semiconductor layer is formed on the first nitride semiconductor layer.

A semiconductor stack including a base substrate; and a PN junction structure including an n-type semiconductor layer on the base substrate and a p-type semiconductor layer on the n-type semiconductor layer, the n-type semiconductor layer being constituted from a group III nitride crystal containing an n-type impurity, the p-type semiconductor layer being constituted from a group III nitride crystal containing Mg as a p-type impurity, and the n-type semiconductor layer and the p-type semiconductor layer constituting a PN junction, or a PI junction structure including an i-type semiconductor layer on the base layer and the p-type semiconductor layer on the i-type semiconductor layer, the i-type semiconductor layer being constituted from a group III nitride, and the i-type semiconductor layer and the p-type semiconductor layer constituting a PI junction.