GaN possesses numerous exceptional properties, such as wide bandgap and high thermal conductivity, which make it an ideal material for fabricating semiconductor devices. The high electric field and current in the channel, coupled with the high power density, make it inevitable that HEMT devices will generate a great deal of heat. Thus, an increase in temperature will unavoidably cause the DC and microwave characteristics of the device to deteriorate. At present, the fourth-generation semiconductor materials with new ultra-broad or ultra-narrow band gaps, mainly Ga₂O₃, GaSb, diamond and AIN, have emerged. In conventional situations, the substrate material will be Si, Sapphire, or the more advanced third-generation material SiC compared to the former, and the passivation layer will use SiN as the material. Our research is in progress to replace the traditional SiN and third-generation SiC with diamond and GaSb.