GaN HEMT (High Electron Mobility Transistor) device and preparation method thereof

The invention relates to the technical field of semiconductor devices, and discloses a GaN HEMT (High Electron Mobility Transistor) device and a preparation method thereof. The GaN HEMT device comprises a substrate, wherein the upper surface of the substrate is sequentially provided with a GaN epitaxial layer and a gate dielectric layer from the bottom up. The GaN HEMT device further comprises a gate electrode, a source electrode and a drain electrode which penetrate through the gate dielectric layer and are contacted with the GaN epitaxial layer. The gate dielectric layer comprises a first gate dielectric layer and a second gate dielectric layer which are different in property, wherein the first gate dielectric layer is provided with a first gate slot, the second gate dielectric layer isprovided with a second gate slot, and the first gate slot corresponds to the second gate slot in position. The gate electrode comprises gate metal fully filling the first gate slot and the second gateslot and a gate cap arran