The use of single-wavelength ellipsometry for the measurement of the temperature of heavily doped and chemically roughened silicon wafers in a rapid-thermal processing (RPT) environment was investigated. At an operating wavelength of 6328 Å, the measurement technique was found to be unaffected by either the substrate doping or surface microroughness of less than 500 Å. Similar results were obtained from room-temperature measurements at other wavelengths. The roughness of the backside of silicon wafers exceeds 500 Å, and the ellipsometric parameter Ψ was observed to decrease with increasing microroughness. Microroughness in excess of 500 Å introduced a systematic error in the temperature measured by ellipsometry that increased in magnitude with increasing surface microroughness. As a result, the unpolished surface of a wafer backside cannot be used to probe for temperature measurement. © 1994, The Electrochemical Society, Inc. All rights reserved.