To get insight into the selective etching of and with respect to InP in alkaline containing solutions, the electrochemical and etching properties of and were studied by rotating (ring)‐disk voltammetry and by electrical impedance and etch rate measurements. It is shown that both and are etched by in an electroless etching process, in which holes are injected by and consumed in the anodic dissolution. The observed selectivity in the etching of and vs. InP is due to a difference in valence band‐edge position, which determines the hole injection rate. Furthermore, it was found that a mechanism of galvanic element formation enhances the selectivity when InP and or InP and are in electrical contact. © 1999 The Electrochemical Society. All rights reserved.