A high electron mobility transistor (HEMT) includes an active region, in which a channel is formed, and a field region surrounding the active region. The HEMT may include a channel layer; a barrier layer on the channel layer and configured to induce a two-dimensional electron gas (2DEG) in the channel layer; a source and a drain on the barrier layer in the active region; and a gate on the barrier layer. The gate may protrude from the active region to the field region on the barrier layer. The gate may include a first gate and a second gate. The first gate may be in the active region and the second gate may be in the boundary region between the active region and the field region. A work function of the second gate may be different from a work function of the first gate.