Multibias and thermal characterizations on 0.25 mu m x (2 x 100) mu m AlGaN/GaN/SiC HEMT and 0.5 mu m x (2 x 100) mu m AlGaAs/InGaAs pseudomorphic HEMT have carried out for the first time. Two competitive device technologies are investigated with the variations of bias and temperature in order to afford a detailed realization of their potentialities. The main finding includes the self heating effect in the GaN device, zero temperature coefficient points at the drain current and transconductance in the GaAs device. The thermal resistance R-TH of 7.1, 8.2 and 9.4 degrees C mm/W for the GaN device was estimated at 25, 75 and 150 degrees C respectively which are consistent with those found in the open literature. The temperature trend of the threshold voltage V-T, Schottky barrier height phi(b), sheet charge densities of two dimensional electron gas ns, and capacitance under the gate C-g are exactly opposite in the two devices; whereas the knee voltage V-k, on resistance R-on, and series resistance R-series are shows similar trend. The multi-bias and thermal behavior of the output current I-ds, output conductance g(ds), transconductance g(m), cut-off frequency f(t), maximum frequency f(max), effective velocity of electron, veff and field dependent mobility, mu demonstrates a great potential of GaN device. These results provide some valuable insights for technology of preference for future and current applications. (C) 2016 Elsevier Ltd. All rights reserved.