A mathematical model describing the combined effect of convective and diffusive mass transport between wafers coupled with a first‐order intrinsic surface reaction for the deposition of polysilicon from silane between two wafers in an annular tube has been formulated. The model incorporates the two extreme cases of surface kinetics and diffusion‐limited regimes as well as the intermediate regime. If the velocity acquires values which are greater than 400 times the diffusion coefficient, the relative curvature of the resulting layer becomes independent of wafer radius. Increasing the wafer spacing leads to less curvature variation of the film. However, the addition of a radial velocity component allows the extension of producing uniform films at higher pressure. Increasing wafer size causes severe reactant depletion problems, if reaction conditions are held constant. A model for diffusivity is formulated based on an equation derived from the kinetic theory of gases. Nucleation in the gas phase is assumed to be unimportant under these conditions.