Using thermal co-evaporation we have prepared epitaxial Cu2ZnSnS4 (CZTS) films on Si(001) substrates. A substrate temperature as high as 370 °C and proper substrate cleaning (HF-dip followed by thermal desorption of surface hydrogens) are found to be necessary for the epitaxial growth. Detailed transmission electron microscopy measurements and X-ray diffraction studies are used to reveal the orientation relation of the CZTS films with the underlying silicon substrate, and the formation of defects within the CZTS layer.