The electrochemical behaviour of a copper coated p-type InP electrode has been investigated. The copper coating was obtained by electrodeposition from a Cu2+ containing sulfuric acid solution under illumination. This reduction reaction can compete with H+ reduction and with its side reaction, the cathodic decomposition of InP, depending on the illumination level, on the Cu2+ concentration in the electrolyte, and on the rotation speed of the electrode. It appears that when the amount of Cu2+ at the InP/electrolyte interface is sufficient to convert the whole flux of the photocarriers, the Cu2+ reduction becomes the main photoprocess, hindering the hydrogen evolution and the cathodic decomposition. A metal deposit up to about 100 equivalent monolayers can form on the electrode surface without any decrease of the photocurrent, as a result of a non-uniform coverage rate of the metal.