Epitaxial thin films of the wide-band-gap chalcopyrite semiconductor CuGaS2 have directly been grown on single crystalline Si substrates of (1 1 1) orientation. Structurally, the samples were characterized by means of reflection high energy electron diffraction, Rutherford backscattering spectroscopy, X-ray diffraction and transmission electron microscopy. The CuGaS2 films crystallize exclusively in the chalcopyrite structure of bulk CuGaS2 material. Metastable cation orderings, which occur in epitaxial layers of similar compounds, are absent. Photoreflectance measurements reveal a fundamental band gap of 2.461(2) eV at 300 chalcopyrite structure is accompanied by the expected crystal-field splitting of K. Moreover, the formation of the highly ordered chalcopyrite the valence band. (C) 2003 Elsevier Science B.V All rights reserved.