A three-dimensional steady-state model of the industry-standard AG Associates 4108 Heatpulse Rapid Thermal Processing system has been developed for the study of thermal uniformity across 8 inch wafers. The model combines radiation energy transfer among all solid surfaces in the chamber with energy transfer among the chamber materials and to the process ambient. Surfaces included are those of the tungsten filaments of the lamps, the silicon wafer, the polysilicon annular thermal guard ring, the quartz process tube, and the gold reflectors which surround the lamps and process tube. These surfaces are divided into approximately 4800 individual surface elements for the radiation transfer allowing very accurate thermal analysis. The model has previously been shown to provide very good agreement with experiment for temperature distributions across an 8 inch wafer. The model is presently used to make quantitative examinations of asymmetric effects occuring in a RTP chamber which cannot be examined by 2-dimensional models. Situations examined include the effect of nonuniform lamp power distributions. Also examined is tilting of the wafer with respect to the flow tube and reflective chamber.