Accurate characterization of the dynamic ON-resistance (RON) degradation is important to predict conduction losses for gallium nitride high-electron-mobility transistors (GaN HEMTs). However, even for the same device, many inconsistent results of dynamic RON based on pulsed measurements are reported in the literature. This letter reveals that insufficient test time leads to spurious dynamic RON results and even contradictory conclusions. We show that the time required for the dynamic RON to stabilize can be very long (~ 3 mins) for some commercial GaN devices and pulsed measurements fail to give accurate results. These findings are enabled by our proposed steady-state method using a hard-switching half-bridge with an active measurement circuit. It minimizes the influence of temperature on the RON, enabling to capture trap-related effects independently from the operation conditions. This work raises awareness of the effect of poorly measured dynamic RON and highlights that steady-state methods should be applied for accurate measurements to predict their performance in real power converter operations.