An electrochemical study of Si/BP heterojunction photoelectrodes was undertaken in order to explore the feasibility of utilizing such electrodes in liquid junction solar cells. It appears that in the case of n-type Si/n-type BP heterostructures, only low photocurrent densities are produced by the electron-hole pairs generated in the wide-bandgap BP window. In contrast, p-type Si/n-type BP heterojunctions show large cathodic photocurrents upon irradiation with visible light. Detailed impedance analysis was carried out to derive the band diagrams of the two studied configurations. It appears that an excellent match between the conduction bands of Si and BP is present, which explains the observed effects. In addition, surface trapping and recombination phenomena at the BP/electrolyte interface were explored with impedance techniques.