A passivation annealing in nitric oxide (NO) ambient significantly reduces the interfacial defects of the SiO2/4H-SiC interface and improves the inversion MOS channel mobility. Effects of the nitridation in NO ambient become more pronounced at high temperatures in general. However, the maximum process temperature in a standard hot-wall oxidation furnace is restricted around 1200oC due to the softening point of quartz. Meanwhile, by use of a cold-wall oxidation furnace, high temperature and short time thermal processes become possible. In this study, we have developed an extremely high temperature (>1400oC) rapid thermal processing for the gate oxidation in the 4H-SiC DIMOSFET fabrication process. The peak MOS channel mobility of lateral MOSFETs on the DIMOSFET chip shows as high as 19cm2/Vs. The specific on-resistance of the device was 12.5mcm2 and the blocking voltage was 950V with gate shorted to the source.