In this work, we study the crystallization and electrical resistivity of the formed oxides in a Cu/SiO2/Si thin film after thermal oxidation by ex-situ annealing at different temperatures up to 1000°C. Upon increasing the annealing temperature, from the X ray diffractogram the phase evolution Cu→Cu+Cu2O→Cu2O→Cu2O+CuO→CuO was detected. Pure Cu2O films are obtained at 200°C, whereas uniform CuO films without structural surface defects such as terraces, kinks, porosity or cracks are obtained in the temperature range 300–550°C. In both oxides, crystallization improves with annealing temperature. A resistivity phase diagram, which is obtained from the current–voltage response, is presented here. The resistivity was expected to increase linearly as a function of the annealing temperature due to evolution of oxides. However, anomalous decreases are observed at different temperatures ranges, this may be related to the improvement of the crystallization and crystallite size when the temperature increases. ► The crystallization and electrical resistivity of oxides in a Cu films are studied. ► In annealing Cu films, the phase evolution Cu+Cu2O→Cu2O→Cu2O+CuO→CuO occurs. ► A resistivity phase diagram, obtained from the current–voltage response, is presented. ► Some decreases in the resistivity may be related to the crystallization.