A direct approach model using the three-dimensional ray-tracing simulation is developed to evaluate the thermal condition in a rapid thermal processing system composed of tungsten/halogen filament lamps, specular reflectors, and the silicon substrate. The paths of the infrared rays emitted from the tungsten/halogen filament lamps are traced following reflections at the surface of the specular reflectors and the polished surface of the silicon substrate. The relationship between the absorbed ray intensities calculated at the silicon substrate and the measured temperatures of the silicon substrate is expressed by the Stefan-Boltzmann law. The effect of a specular reflector tube installed in the rapid thermal processing system is evaluated based on the temperature profiles and the absorbed ray intensities calculated over the silicon substrate. It is concluded that the temperature profile over the silicon substrate can be predicted using the model developed in this study.