We have investigated growths of 3C-SiC/Si multilayer heterostructures on Si(100) by supersonic free jet CVD. CH3SiH3 and Si3H8 gas jets were used for 3C-SiC and Si layer growth, respectively. The crystal quality of Si layers on 3C-SiC/Si(100) was found to strongly depend on the 3C-SiC surface roughness. Polycrystalline Si was grown on rough 3C-SiC layers with a thickness of 9 nm, while epitaxial Si was grown by using ultrathin (approximate to3 nm) 3C-SiC layers with smooth surfaces. Epitaxial 3C-SiC/Si/3C-SiC/Si(100) heterostructures were successfully obtained on ultrathin 3C-SiC/Si(100).