A high electron mobility transistor (HEMT) includes a buffer layer on a substrate, a barrier layer on the buffer layer, a gate electrode on the barrier layer, a first passivation layer adjacent to two sides of the gate electrode, and a p-type semiconductor layer between the gate electrode and the barrier layer. Preferably, a corner of the p-type semiconductor layer contacting a sidewall of the first passivation layer includes a first curve, and a bottom surface of the p-type semiconductor layer directly on the first passivation layer includes a second curve.