In this paper an advanced numerical approach for the simulation of epitaxial growth in metalorganic chemical vapor deposition reactors (MOCVD) is presented. The mathematical model is based on the conservation equations for momentum and heat transfer combined with mass transfer including thermodiffusion and chemical reactions. The thermal radiation analysis assumes a non-participating medium and semi-transparent quartz walls. The radiation heat transfer is coupled with convection and conduction. The heat conduction includes thermal solid/fluid interactions between the gas and solid parts of the reactor. The model is implemented in a finite volume numerical solution procedure on block-structured non-orthogonal grids for two-dimensional (plane and axisymmetric) laminar flows. To speed up the convergence of the computations, a @'full approximation scheme@' multigrid technique is employed. In order to demonstrate the ability of the present method to analyze complex problems, investigations for horizontal CVD reactor configurations are presented. These problems include very complicated radiative heat transfer, buoyancy-driven flow, combined heat transfer in the reactor walls and the susceptor, as well as the transport of chemically reacting components. The simulated temperature distribution is compared with well-known temperature measurements and good agreement with them is achieved. The growth of GaAs from trimethylgallium (TMGa), arsine, and hydrogen was considered where the deposition process is assumed to be in the transport-limited regime. The predicted deposition rates in the reactor fairly well compare with the available experimental results from literature.