In this review paper, we explain the apparent opposite behaviors observed in surface reactivities of semiconductors such as phosphide and arsenide compounds invoked in several interfacial and electrochemical reactions: anodic dissolution, selective etching cathodic decomposition and passivation process. The Semiconductor / Electrolyte interfaces have been used to have a better accuracy in the determination of surface and interface processes (nature, energy position and density of surface states). Dissolution process has been investigated and the opposite behaviors of GaAs and InP compounds have been explained by the preferential chemical activity of phosphorus element. Passivation of semiconductor compounds has been investigated and principally the specificity of InP which has been studied in presence of hydrogen evolution reaction in acid aqueous media. Cathodic decomposition exists for all In-V binary and ternary compounds. The specific influence of proton has been demonstrated in the cathodic corrosion mechanism, which is always a conduction band machanism. The specifity of some III or V elements have been carried out in typical interface reactions. The surface modification has been investigated by coupling electrochemical and electro-optical techniques. These “in-situ” techniques are competitive in relation to surface analysis “ex-situ” techniques such as X-ray Photoelectron Spectroscopy (XPS). Our purpose in this paper is also to demonstrate that electrochemical and electro-optical “in-situ” techniques are very suitable for investigations and analysis of surface and interface semiconductor properties.