The electrodeposition of copper from acidic chloride and sulfate solutions onto the surface of n- and p-GaAs electrodes and the dissolution of copper from the GaAs surface have been studied by means of cyclic voltammetry, rotating-ring-disk voltammetry and impedance measurements. The results show, that the reduction of Cu2+ is due to the injection of holes. In chloride solutions, reduction to Cu+ precedes the reduction to Cu-0, whereas in sulfate solutions no Cu+ intermediates are detected. At open-circuit potential, Cu2+ is reduced to Cu+ in chloride solutions, Cu2+ hence being an electroless etchant for GaAs. At p-GaAs, dissolution of copper by holes is observed both in Cl- and SO42- medium, whereas at n-GaAs in chloride solutions, copper is seen to dissolve chemically. Mechanisms explaining the observed potential-dependence of the hole injection rate are proposed, and the morphology of the copper layers as well as the electrical properties of the resulting GaAs/Cu dry junctions are discussed.