Experimental measurements of wafer temperature in a single-wafer, lamp-heated chemical vapor deposition system were used to study the wafer temperature response to gas composition. A physically based simulation procedure for the process gas and wafer temperature was developed in which a subset of parameter values were estimated using a nonlinear, iterative parameter identification method, producing a validated model with true predictive capabilities. With process heating ramp power held constant, wafer temperature variations of up to 160 K were observed by varying the feed gas H-2/N-2 ratio. Heat transfer between the wafer and susceptor was studied by shifting the instrumented wafer off the susceptor axis, exposing a portion of the wafer backside to the chamber floor. Model predictions and experimental observations both demonstrated that the gas velocity field had little influence on the observed wafer and predicted gas temperatures.