A long-term 3000-hour test under on-state conditions (V DS =25V, 6W/mm constant dissipated power) and off-state conditions (V DS =46V, V GS =-6V) on GaN/AlGaN/GaN HEMTs is presented. Trapping presence and hot-electrons effect are characterized by means of low-frequency techniques (lowfrequency noise measurements, transconductance frequency dispersion, gate-lag). The on-state stress shows the most important degradation. Since our measurements point out to the creation of traps in the gate-to-drain surface region during the stress, this degradation is ascribed to the effect of hotelectrons.

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