The present application discloses a planar High-Electron-Mobility Transistor (HEMT), which includes a hetero-junction consisting of a first semiconductor epitaxial layer and a second semiconductor epitaxial layer, and two-dimensional electron gas located at an interface of the hetero-junction; a bottom surface of a gate trench of a trench gate is located at a bottom of the two-dimensional electron gas to cut off the two-dimensional electron gas; when gate-source voltage is higher than or equal to threshold voltage, an inversion layer is formed on a surface of the first semiconductor epitaxial layer covered by side surfaces and a bottom surface of a gate conductive material layer, and the source-end and drain-end two-dimensional electron gas is conducted to enable the device to be on; when the gate-source voltage is lower than the threshold voltage, the source-end and drain-end two-dimensional electron gas is cut off to enable the device to be off.