Engineering models, based on computational fluid dynamics, have been developed and used to improve the performance of two metalorganic chemical-vapor-deposition reactors. Though the knowledge of the chemical reactions occurring during film deposition is incomplete, the models provide insight into the reactor’s performance and are useful in guiding reactor modifications. In one reactor, the effect of three gas injector designs on the film thickness uniformity is examined; in a second reactor, the shape and placement of a flow deflector, which redistributes the flow of gas over the wafer surface, is studied. In both cases, comparing the experimental results obtained both before and after the reactor modifications, significant improvements in film thickness uniformity were realized.