In this paper results obtained by drain current transients measurement on GaN-based high electron mobility transistors (HEMTs) are presented. It will be shown that neglecting device self-heating effects during the calculation process can lead to an underestimation of said energies and to non-overlapping Arrhenius plots, when the emission time constants are extracted at different device dissipated power levels. Thanks to the estimation of the mean channel thermal resistance, thermal effects were taken into account by correcting the measured data. Higher activation energy values have then been extracted and a reasonable overlap of the Arrhenius plots was obtained amongst measurements carried out at different dissipated powers. The experimental results are also suggesting a novel method for the extraction of device thermal resistance, which yielded similar results with respect to other experimental techniques. © 2013 IEEE.