Apparatus and methods of thermally treating a wafer or other substrate, such as rapid thermal processing (RTP) apparatus and methods are disclosed. An array of radiant lamps directs radiation to the back side of a wafer to heat the wafer. In one or more embodiments, the front side of the wafer on which the patterned integrated circuits are being formed faces a radiant reflector. In one or more embodiments, the wafer is thermally monitored for temperature and reflectivity from the side of the reflector.