Interface state density and channel mobility have been characterized for 4H-SiC MOSFETs fabricated with dry thermal oxides and subsequently passivated with nitric oxide. The interface trap density at 0.1 eV below the conduction band edge decreases from approximately 8 x 10(12) to 1 x 10(12) eV(-1) cm(-2) following anneals in nitric oxide (NO) at 1175 degreesC for 2 h. The room temperature field effect channel mobility increases by an order of magnitude to approximately 35 cm(2)/V s following the passivation anneal. The field effect channel mobility of passivated MOSFETs shows almost no change with increasing temperature, while the mobility for unpassivated devices increases with increasing temperature and is thermally activated (similar toT(1.9)) due to decreased Coulomb scattering by electrons trapped at the acceptor-like interface states near the conduction band. Over the temperature range 300-473 K, threshold voltage changes of about -0.8 and -3.7 V, respectively, are observed for devices processed with and without NO passivation.