The electrochemical deposition of copper from a copper sulfate solution at (100) p-GaAs is investigated by means of cyclic voltammetry and chronoamperometry. The kinetics of the reduction of Cu2+ to Cu-0 are found to be different at a bare p-GaAs substrate as compared to those at a substrate covered with an amount of copper which is the equivalent of a fraction of one monolayer to a few monolayers. Furthermore, a minimum submonolayer of copper is necessary for bulk copper deposition to occur. From the results a reaction mechanism, involving hole injection mediated by metal-induced surface states is proposed. The filling of surface states causes a shift of the bandedges, initiating bulk reduction. The initial amount of copper (monolayer) determines the density of metal-induced surface states and hence the bulk deposition rate.