The axi-symmetric vertical reactor is a classical reactor configuration for the growth of compound semiconductors by MOCVD. In the present study, the modified reactor is developed to produce uniform and large-volume epitaxial deposition of gallium nitride (GaN). A comprehensive knowledge of the flow, thermal and concentration fields, as well as gas surface reaction, is necessary to develop a CVD reactor. The full elliptic governing equations for continuity, momentum, energy and chemical species are solved numerically. It is investigated how thermal characteristics, reactor geometry, and the operating parameters affect flow fields, mass fraction of each reactant, and deposition rate uniformity. As results, inlet flow rate, inclination angle of wall and inlet design are proposed for optimum operational conditions. (C) 2002 Elsevier Science B.V. All rights reserved.