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 hafnium oxide dielectric layer, a source, a drain, a grid, an insulation layer and a field plate metal layer, wherein the hafnium oxide dielectric layer is arranged on the GaN epitaxial layer, the source, the drain and the grid are arranged on the dielectric layer, penetrate through the dielectric layer and are connected with the GaN epitaxial layer, the insulation layer is arranged on the source, the drain, the grid and the dielectric layer, and the field plate metal layer is arranged on the insulation layer. 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.