The effect of the crystal quality and surface morphology on the electrical properties of MOS capacitors has been studied in devices manufactured on 3C-SiC epitaxial layers grown on Silicon (100) substrate. The interface state density, which represents one of the most important parameters for the 3C-SiC MOSFET development, has been determined through capacitance measurements. A cross-correlation between High Resolution X-ray Diffraction, AFM analysis and electrical conductance measurements has allowed determining the relationship between the crystalline quality and the interface state density. By improving the crystalline quality, a decrease of the interface state density down to 10 10 cm-2 eV-1 was observed.