The optical properties of epitaxial CuchiGaySe2 layers were studied in dependence of composition and temperature by photoreflectance (PR) spectroscopy and were compared to the results of photolummescence (PL) studies. The three valence-split bands, E-a, E-b and E-c, were intensively present in the PR-spectra of stoichiometric and Cu-rich layers, and weakly present in the spectra of Ga-rich layers. From the temperature-dependent PR-spectra, the phonon excitation energy for carrier scattering on phonons was calculated to (29+/-2) meV in agreement with the PL-results. From the composition-dependent PR-spectra strain effects were quantified: the contribution of the strain induced by a microcrystalline CuxSe-phase on the surface of Cu-rich layers in the overall strain of the layer was estimated to 13% for [Cu]/[Ga] = 1.80. (C) 2003 Elsevier B.V. All rights reserved.