3C-SiC lattice parameters, both in-plane and out-of-plane, have been studied as a function of the temperature (up to 773 K) by performing X-Ray Diffraction (XRD) measurements in coplanar and non-coplanar geometry during the thermal treatments. A tetragonal distortion of the 3C-SiC cell has been observed, with a= b≠ c, resulting from a tensile stress status induced by the presence of Si substrate. A linear expansion coefficient of about 4.404× 10-6 K-1 at 773 K has been obtained for a 15 μm thick 3C-SiC film grown on (100) Si substrate. The discrepancy with the value reported in literature of 5.05× 10-6 K-1 at 800 K [Slack et al., Journal of Applied Physics 46, 89 (1975)] may be related to the different nature of samples used.