In recent years, significant progress has been made in the development of domestic 6-inch SiC-based Gallium Nitride High Electron Mobility Transistors (GaN HEMTs). This paper investigates the multi-layer dielectric stress modulation technique and high-consistency backside etching technique, which are integrated into the 6-inch process. When operating at 48 V, the 0.5 μm process achieves an output power density of 8.6 W/mm at 3.5 GHz, with a power gain of 15 dB and a Power Added Efficiency (PAE) of 58.5%. When operating at 28 V, the 0.25 μm process achieves an output power density of 5.5 W/mm at 10 GHz, with a power gain of 8.7 dB and a PAE of 55.2%. The reliability of GaN devices is evaluated through High-Temperature Operating Life (HTOL) and High-Temperature Reverse Bias (HTRB) tests, with the saturation output current of the devices changing by less than 10% after 1 000 hours. The 20 W and 40 W power transistors, as well as X-band Monolithic Microwave Integrated Circuit (MMIC) power amplifiers, are fabricated to validate the process technology, with measured on-wafer yields of 90%, 86%, and 77%, respectively. The results indicate that domestic 6-inch SiC-based GaN HEMTs have application potential below the Ku-band.