A high electron mobility transistor (HEMT) includes a channel layer, a plurality of barrier layers, and a p-type semiconductor layer. The barrier layers have an energy band gap greater than that of the channel layer. A gate electrode is arranged on the p-type semiconductor layer. A source electrode and a drain electrode are apart from the p-type semiconductor layer and the gate electrode on the barrier layers. Impurity concentrations of the barrier layers are different from each other in a drift area between the source electrode and the drain electrode.