A nitride semiconductor device includes a transistor having a semiconductor stacked body formed on a substrate, and a pn light-emitting body formed on the semiconductor stacked body. The semiconductor stacked body includes a first nitride semiconductor layer, and a second nitride semiconductor layer formed on the first nitride semiconductor layer and having a bandgap wider than that of the first nitride semiconductor layer. The transistor includes: the semiconductor stacked body; a source electrode and a drain electrode formed away from each other on the semiconductor stacked body; and a gate electrode provided between the source electrode and the drain electrode and formed away from the source electrode and the drain electrode. The pn light-emitting body includes a p-type nitride semiconductor layer and an n-type nitride semiconductor layer to emit a light beam having an energy value higher than an electron trapping level existing in the semiconductor stacked body, in which the p-type nitride semiconductor layer of the pn light-emitting body is electrically connected to the gate electrode, and functions as a gate of the transistor.