Activation energy of drain-current degradation in GaN HEMTs under high-power DC stress.

•We have observed two sequential degradation mechanisms for GaN HEMTs under high-power stress at high temperature.•Saturation of gate leakage degradation appears to be necessary for the emergence of significant drain current degradation.•We have developed a new methodology to extract activation energy of GaN HEMT degradation rate from measurements on a single device. For this, we use step-temperature stress experiments.