We present a systematic approach to the modeling of rapid thermal processing systems. In this approach, a discretized version of a computer-aided design file of a rapid thermal processing system is incorporated into fundamental physically based models of the transport phenomena to aid in design and optimization of these reactors. These models include a detailed radiative-heat-transfer description which is used to compute radiative exchange factors involving both diffuse and specular surfaces. The radiative exchange factors are then incorporated into transient finite element fluid-flow and heat-transfer models to investigate effects of conductive and convective heat transfer on wafer temperature uniformity. This approach is illustrated in investigations of the effects of thermal guard rings and radiative properties of the chamber on wafer temperature uniformity. Comparisons are made with experiments, and reduced-complexity models are evaluated to identify their range of applicability.