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 angstrom, the measurement technique was found to be unaffected by either the substrate doping or surface microroughness of less than 500 angstrom. Similar results were obtained from room-temperature measurements at other wavelengths. The roughness of the backside of silicon wafers exceeds 500 angstrom, and the ellipsometric parameter psi was observed to decrease with increasing microroughness. Microroughness in excess of 500 angstrom 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.