This paper describes a nitrogen-based passivation technique for interface states near the conduction band edge in 4H-SiC/SiO2. These states were first proposed by Schorner, et al. [1], and their origin remains a point of discussion. However, there is now general agreement that these states are largely responsible for the lower channel mobilities that are reported for n-channel, inversion mode 4H-SiC MOSFETs. A post-oxidation anneal in nitric oxide at atmospheric pressure, 1175degreesC and 200-400sccm for 2hr reduces the interface state density at E-c- E congruent to 0.1 eV by more than one order of magnitude to approximately 2x10(12)cm(-2)eV(-1). The effective channel mobilitiy for lateral n-channel 4H-MOSFETs increases correspondingly from single digits to approximately 30-40cm(2)/V-s. The mobility for passivated devices exhibits a very weak temperature dependence compared to unpassivated devices for which the mobility increases in proportion to temperature to the power 1.9. The NO passivation process does not significantly affect the breakdown characteristics of thermal oxides on n- and p-4H-SiC, and the beneficial effects of passivation survive post-passivation processing procedures such as the high temperature anneals that are required to form source/drain ohmic contacts.