The Monte Carlo method has been applied to simulate the CH4-H-2 reactive ion etching process for an atomic scale InP surface. Two neutral precursor types and one ionic precursor type have been considered in the surface etching process. CH3 and H adsorbed radicals are assumed to be bonded to the surface substrate leading to the ejection of indium and phosphorous sites, respectively, whereas energetic ions induce the In(CH3)(x) and P(H)(x) (x = 0,1,2,3) ejection from the surface. The model takes into account precursor and site identities, physisorption, chemisorption, migration and desorption of etchant neutrals, chemical etching, and ion preferential sputtering of sites. The chemisorption probability effects of the neutral precursors on the rms roughness, the etching rate, and the phosphorus depletion are shown. On the other hand, the increase of the ion flux allows an increase in rms roughness. By setting the available experimental data, the simulation results confirm the existence of the phosphorus depleted surface layers, which were previously observed by x-ray photoelectron spectroscopy analyses.