Thermal and small-signal model parameters analysis have been carried out on 0.5 mu m x (2 x 100 mu m) AlGaAs/GaAs HEMT grown on semi-insulating GaAs substrate and 0.25 mu m x (2 x 100 mu m) AlGaN/GaN HEMT grown on SiC substrate. Two different technologies are investigated in order to establish a detailed understanding of their capabilities in terms of frequency and temperature using on-wafer S-parameter measurement over the temperature range from -40 to 150 degrees C up to 50 GHz. The equivalent circuit parameters as well as their temperature-dependent behavior of the two technologies were analyzed and discussed for the first time. The principle elevation or degradation of transistor parameters with temperature demonstrates the great potential of GaN device for high frequency and high temperature applications. The result provides some valuable insights for future design optimizations of advanced GaN and a comparison of this with the GaAs technology. (C) 2016 Elsevier Ltd. All rights reserved.