In this work a comparison between different 6 inches 4H-SiC commercial substrates after post processing has been shown. The main comparison was done between two different suppliers after a thinning process that leaves the sample with a final thickness of 150 microns. After the processing the two substrates show different behavior with different curvature and residual stress. X-Ray diffraction show different crystal quality and curvature values of the substrates. Micro-Raman show different residual stress of the substrates before and after the thinning process. Moreover, molten KOH etching for dislocation detection also show different value of dislocation density for both substrates.