The electrochemistry and the etching of monocrystalline p- and n-InP in alkaline K3Fe(CN)6 solutions were studied by rotating disc electrode, rotating ring-disc electrode, optoelectrical impedance and analytical techniques. The etching process was found to consist of two compensating partial currents, corresponding to the cathodic reduction of Fe(CN)(6)3- via hole injection and to the anodic dissolution of InP respectively. The rate of the former reaction was found to depend on the polarization of the electrode. The latter reaction was studied in detail by performing optoelectrical impedance experiments and by measuring the relationship between the electron injection current and the hole injection current at n-type electrodes. A difference in surface morphology after etching was observed between the (111) face, on the one hand, and the (111BAR) and (100) faces on the other hand.