Preparation method of source field plate of GaN-based HEMT device and HEMT device

The invention provides a preparation method of a source field plate of a GaN-based HEMT device and the HEMT device suitable for the technical field of semiconductors. The method comprises that a SiN layer in a first thickness and a SiO2 layer in a second thickness are grown in the upper surface of the device successively; a part corresponding to a first area is removed from the SiO2 layer; the surface, toward a gate electrode region, of a part, corresponding to a second gate-drain area, in the residual area of the SiO2 layer is an inclined surface with a first inclination angle; parts corresponding to the source and drain electrode regions are removed from the SiO2 layer as well as the SiN layer successively; a metal layer in a third thickness is grown in a part, corresponding to a sourcefield plate area, in the upper surface of the device; and the metal layer covers the inclined surface of the part, corresponding to the second gate-drain area, of the SiO2 layer. The field plate prepared by the method is of a