HEMT device and preparation method thereof

The invention provides an HEMT (High Electron Mobility Transistor) device and a preparation method thereof, the HEMT device comprises a substrate, a laminated structure, a first dielectric layer, a gate conductive layer, a second dielectric layer, a drain contact hole, a gate contact hole, a drain, a gate and a source, and a groove is formed in the substrate; the laminated structure comprises a channel layer and a barrier layer and covers the exposed surface of the groove and the upper surface of the substrate; the first dielectric layer fills the groove and covers the laminated structure, and a gate hole is formed in the first dielectric layer; the gate conductive layer fills the gate hole; the second dielectric layer covers the first dielectric layer and the gate conductive layer. The drain contact hole penetrates through the second dielectric layer, the bottom surface of the drain contact hole at least exposes the barrier layer above the substrate, and the gate contact hole penetrates through the second di