GaN semiconductor device and fabrication method thereof

The invention relates to the technical field of a semiconductor material, and provides a GaN semiconductor device. The GaN semiconductor device comprises a GaN epitaxial layer, a composite dielectric layer, a source, a drain, a grid and an insulation layer, wherein the composite dielectric layer is arranged on the GaN epitaxial layer, the source, the drain and the grid are arranged on the composite dielectric layer, penetrate through the composite dielectric layer and are connected with the GaN epitaxial layer, the insulation layer is arranged on the source, the drain, the grid and the composite dielectric layer, and the material of the insulation layer is silicon dioxide. By the GaN semiconductor device, an aluminum nitride Ga layer is difficult to break down, the problems of electric leakage and breakdown occurring in the GaN semiconductor device are further prevented, the GaN semiconductor device is effectively protected, and the reliability of the GaN semiconductor device is improved.