The nano-characterization of thermal oxides grown on 4H-SiC is for the first time presented and analysed to derive its reliability. The dielectric breakdown (BD) kinetics of silicon dioxide (SiO2) thin films thermally grown on 4H-SiC has been determined by comparison between I-V measurements on large-area (up to 1.96×10-5 cm2) metal-oxide-semiconductor (MOS) structures and conductive atomic force microscopy (C-AFM) with a resolution of a few nanometers. C-AFM clearly images the weak breakdown single spots under constant voltage stresses. The stress time on the single C-AFM tip dot has been varied from 1×10-3 to 1×10-1 s. The density of BD spots, upon increasing the stress time, exhibits an exponential trend. The Weibull slope and the characteristic time of the dielectric BD events were so determined by direct measurements at nanometer scale demonstrating that the percolation model is valid for thin thermal oxide layers on 4H-SiC (5-7nm), but it fails for larger thicknesses (10 nm).