Silicon epitaxial growth with SiH2Cl2 (DCS) is modeled within a realistic thermal-fluid environment using a detailed reaction mechanism. The proposed reaction mechanism includes both gas-phase and surface reactions. It accounts for surface-adsorbed species and individual surface coverages to predict deposition rates. The predicted deposition rates are compared to measured growth rates at different temperatures, pressures, and DCS flow rates. The agreement between predicted and measured growth rates is found to be very good. The suggested reaction mechanism is based on two reaction pathways. First, DCS adsorbs directly on the Si surface and decomposes there while desorbing H-2, HCl, and SiCl2. Second, at temperatures above 800 degrees C the thermal activation gets high enough to allow the pyrolysis of DCS to SiCl2 and H-2 in the gas phase. The generated SiCl2 reacts on the silicon surface, representing the second deposition pathway. The two reaction pathways are valid for all temperatures. The dominance of one or the other pathway at a given temperature results self-consistently from the different thermal activation of the individual chemical reactions involved.