Different types of surface pre-treatments of galena electrodes, chosen on the basis of literature data, lead to different behaviours in the time dependence of impedance spectra. The results show the influence of a damaged layer due to mechanical polishing. The same equivalent circuit is found whatever the pre-treatment even in the range of positive potentials where oxidation of galena occurs. As in previous studies, the potential dependence of the capacitance shows that natural galena is an n-type semiconductor. However, the photocurrent is negative. Its potential dependence is bell-shaped, suggesting the effect of a process similar to passivation. Some similarities in behaviour are noted between the impedance in the lower frequency range (<1 kHz) and the photocurrent obtained with modulated illumination.