When we were qualifying GaN HEMT power stages for hard-switching applications, the screen that actually correlated with RDS(on) drift in the field wasn't a traditional high-temperature operating life soak or simple HTRB. What stood out for us was dynamic power cycling under realistic switching loads with elevated junction temperature swings. Static stress tests at constant temperature really don't stress the mechanisms that drive dynamic RDS(on) drift in GaN, because those drifts are tied to trapping/detrapping and gate interface charge movement under high dV/dt and gate bias swing. The single condition that gave us the sharpest early indication was power cycling with a sustained high gate bias (VG = +7 V), a negative off-state bias (VG = -3 V), and hard switching at elevated junction temperatures (~150 degC), dwelling with minimal dead-time so the device saw continuous charge and discharge stress. We ran this at realistic load currents and duty cycles that mirrored the worst case we expected in customer systems. What I found most telling was the long off-state dwell at negative bias combined with high temperature and frequent switching. That combination accelerated the very trapping/detrapping and interface state changes that eventually manifested as RDS(on) drift in fielded units. After a few thousand cycles, the devices that would show drift later in the field had already started to show slight but measurable increases in dynamic RDS(on). As a result, we changed our qualification plan to include this dynamic power cycle screen as a gatekeeper test, not just at the end of qualification but early during engineering samples. It helped catch marginal lots early, reduced field escapes, and gave engineering better feedback on how design changes affected reliability.