Metalorganic Vapor Phase Epitaxy (MOVPE) has emerged as the technique of choice for growing thin films and structures of group III-nitrides. The objective of this work is to address the optimal design of vertical rotating disk and stagnation flow MOVPE reactors in order to achieve film thickness uniformity over large area substrates. Gas inlets that preserve the axial symmetry and enable alternating feeding of the precursors through coaxial rings were studied. The growth of GaN films from trimethyl-gallium and ammonia was used as a typical example. A fundamental reaction-transport model of the MOVPE process including gas-phase reactions and gas-surface interactions has been developed. The model was validated through comparison with growth rate data obtained from both research-scale and industrial-scale reactors. Performance diagrams for industrial-scale stagnation flow and rotating disk reactors were developed by varying the reactor geometry and operating conditions to identify regions of uniform film growth.