Temperature measurement and heat-treating methods and systems. One method includes measuring a present intensity of radiation thermally emitted from a first surface of a workpiece, and identifying a present temperature of the first surface in response to the present intensity and at least one previous thermal property of the first surface. Preferably, the workpiece includes a semiconductor wafer, and the first and second surfaces respectively include device and substrate sides thereof. The present temperature of the device side is preferably identified while the device side is being irradiated, e.g. by an irradiance flash having a duration less than a thermal conduction time of the wafer. The device side temperature may be identified in response to a previous device side temperature, which may be identified in response to a previous temperature of the substrate side unequal to the previous device side temperature, and a temperature history of the wafer.