This letter demonstrates that GaN-based MIS-HEMTs submitted to stress with high-temperature, high drain bias, and constant source current (HTSC stress) may show degradation modes that are not detectable during standard high temperature reverse bias (HTRB) stress. Based on a number of stress/recovery experiments, we demonstrate the following novel results: 1) the combined presence of high drain bias and constant drain–source current (HTSC stress) can lead to a significant increase in ON-resistance ( $R_{\mathrm{\scriptscriptstyle ON}}$ ) that is not detected under conventional HTRB stress; 2) $R_{\mathrm{\scriptscriptstyle ON}}$ increases without changes in the threshold voltage, indicating that charge trapping takes place in the access regions, and not under the gate; 3) the $R_{\mathrm{\scriptscriptstyle ON}}$ increase has a monotonic dependence on the source current flowing during stress; and 4) for the same stress current level, the $R_{\mathrm{\scriptscriptstyle ON}}$ increase has a negative dependence on temperature. The strong correlation between $R_{\mathrm{\scriptscriptstyle ON}}$ increase and source current and the negative temperature coefficient strongly support the hypothesis that trapping originates from the injection of hot electrons toward the gate–drain access region.