The channel mobility in SiO 2 /GaN hybrid metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs) has been studied. The formalism used for the inversion mobility in MOSFETs has been adapted to the case of GaN MOS-HEMTs, which operate in accumulation condition. Using the values of interface trapped charges (Q trap = 1.35 × 10 12 cm -2 ) and surface roughness (RMS = 0.15 nm) determined by capacitance-voltage-measurements and nanoscale morphological analyses allowed to derive meaningful physical parameters for the mobility model. The temperature dependence of the peak mobility-that decreases from 110 cm 2 V -1 s -1 at room temperature down to 91 cm 2 V -1 s -1 at 423 K-is mainly ruled by phonon and Coulomb scattering effects. The implications in practical devices were discussed, considering the possible improvement of the device on-resistance that can be obtained by …