Temperature control during rapid thermal processing continues to be subjected to pressures for improved reliability by advanced semiconductor device manufacturing requirements. A very simple, inexpensive, and compact temperature sensor, based on the temperature dependence of the reflectivity of materials, has been developed here at IBM. While this sensor is directly applicable to metals, semiconductors, and insulators, we emphasize here only application to silicon, for which the optical reflectance thermometer (ORT) is continuously applicable from well below room temperatures to the melting point with a response time of less than 1 ms. The operation of this thermometer is demonstrated in a conventional rapid thermal anneal (RTA) chamber. When the RTA temperature cycle is controlled by the ORT, repeatability of±3 °Cis routinely obtained for steady-state dwell times as short as 0.4 s at 987 °C and slew rates as high as 445 °C/s. The actual sample temperature is continuously recorded as a function of time.