The crystal structure of the wurtzite-derived beta-CuGaO2 was refined by Rietveld analysis of high-resolution powder diffraction data obtained from synchrotron X-ray radiation. Its structural characteristics are discussed in comparison with the other I-III-VI2 and II-VI oxide semiconductors. The cation and oxygen tetrahedral distortions of the beta-CuGaO2 from an ideal wurtzite structure are small. The direct band-gap nature of the beta-CuGaO2, unlike beta-Ag(Ga,Al)O-2, was explained by small cation and oxygen tetrahedral distortions. In terms of the thermal stability, the beta-CuGaO2 irreversibly transforms into delafossite alpha-CuGaO2 at >460 degrees C in an Ar atmosphere. The transformation enthalpy was approximately -32 kJ mol(-1), from differential scanning calorimetry. This value is close to the transformation enthalpy of CoO from the metastable zincblende form to the stable rock-salt form. The monovalent copper in beta-CuGaO2 was oxidized to divalent copper in an oxygen atmosphere and transformed into a mixture of CuGa2O4 spinel and CuO at temperatures >350 degrees C. These thermal properties indicate that beta-CuGaO2 is stable at =300 degrees C in both reducing and oxidizing atmospheres while in its metastable form. Consequently, this material could be of use in optoelectronic devices that do not exceed 300 degrees C.