In this paper, we demonstrate the unique ability of a newly developed slow-trap profiling technique to characterise silicon-based MOS capacitors in strong inversion. We also demonstrate the applicability of the slow-trap profiling technique for the characterisation of oxides grown on SiC. The obtained slow-trap profiles show that NO nitridation eliminates while N2O creates defects acting as slow traps in the case of both Si and SiC substrates. The corresponding effects of nitridation on interface traps and fixed oxide charge are also discussed.