In acidic Liquid ammonia solutions, the cathodic decomposition of n-InP occurring during hydrogen evolution is similar to that in aqueous systems. This decomposition results in the formation of art indium layer on the surface for a cathodic bias in the potential range where protons are reduced. A characteristic anodic peak is observed in the following positive-potential scan and is associated with the anodic dissolution of the surface indium. The identity of this peak was verified by the electrochemical behavior of Inp and smooth Pt electrodes coated with an indium film, prepared by the reduction of In3+ on the Electrodes in liquid ammonia. These results suggest that a strong interaction of hydrogen atoms with the InP surface takes place during the first step of the reduction of protons, regardless of their solvation (H2O or NH3).