The growth of thick and high quality epitaxial 4H-SiC layers requires a good control of the CVD process. An horizontal hot-wall reactor commercialized by the Epigress company is used. The precursors are silane and propane diluted in hydrogen. The typical temperature range is 1700-1900 K and the pressure fixed at 250 mbar. Modeling and numerical simulation are used to better understand the intricate mixture of phenomena involving electromagnetics, heat, mass transfer and reactivity in different geometries and experimental conditions [1-4]. 3D modeling and simulation of electromagnetics and heat transfer have been previously presented for this reactor [1]. In this paper, a chemistry model including surface deposition and hydrogen etching is first described. Finally, experiments and measurements are compared to simulation results to validate the model and to reveal the problems related to high temperature technology and large-scale area growth.