0.25 ?m gate AlGaN/GaN/SiC HEMT'snonlinearity modelling and characterization over a widetemperature and frequency have been studied for the first time.The nonlinearity of these devices has been carried out using atwo-tone intermodulation distortion. An empirical analyticalmodel has been developed and good agreement was establishedbetween the simulated and measured data. This result is valuablefor the future design optimizations of the advanced GaN basedMMIC?s operating at high temperature.