An improved system and method of measuring the temperature of a workpiece being processed is disclosed. The temperature measurement system determines a temperature of a workpiece by measuring the amount of expansion in the workpiece due to thermal expansion. The amount of expansion may be measured using a number of different techniques. In certain embodiments, a light source and a light sensor are disposed on opposite sides of the workpiece. The total intensity of the signal received by the light sensor may be indicative of the dimension of the workpiece. In another embodiment, an optical micrometer may be used. In another embodiment, a light sensor may be used in conjunction with a separate device that measures the position of the workpiece.