A multiscale approach has been developed in order to simulate the etch process of InP in an inductive coupled plasma (ICP) Cl2/Ar plasma discharge. The model consists of three modules: a global kinetic model of the Cl2/Ar plasma discharge, a sheath model, and a 2-D Monte-Carlo etching model. The densities and the fluxes of all neutral and charged species considered in the reaction scheme as well as the electron temperature are calculated from the global model. The angular and energy distribution functions of ions are computed from the sheath model. The output parameters of both the global kinetic model and the sheath model in terms of particle fluxes, ion angular distribution function and ion energy distribution function are used as input parameters in the 2-D etching model. The latter allows tracking in time the evolution of the etched surface. The ultimate goal of the multiscale approach is to predict the etch rate, the etched surface chemical composition, and the etch profile as a function of the operating conditions (power, pressure, gas flow rates, etc). In this paper, the results from the global model are first compared to the measurements carried out in the ICP etching tool, showing a satisfactory agreement. The etching model is then used to simulate the etching of narrow trench and small-diameter hole in InP. The mechanisms involved in the development of undercut below the mask and in the bowing effect are analyzed. The comparison between simulated and experimental etch profiles evidences the important role of Cl adsorption probability on the development of the undercut, and the significant impact of the redeposition of the etched species on the etch rate variation and on the narrowing in the bottom of the etched hole/trench.