4H- and 6H-SiC On Insulator structures (SiCOI) are successfully obtained using the Smart-Cut(R) process. As previously published [1,2], initial SiCOI samples exhibited an unacceptable high resistivity due to deep levels generated by implantation of large dose of protons required to induce thin film exfoliation. Hall effect measurements and EPR (Electron Paramagnetic Resonance) measurements were performed to determine the concentration and the microscopic structure of the compensating defects in layers obtained as the process conditions evolve. From the resistivity variation with temperature the activation energy of the compensating defect pinning the Fermi level is found to be 500 meV. The compensating defect content, as extracted by Hall effect measurement analysis, has been lowered down to a few 10(16) cm(-3) since the process reached maturity.