In light-irradiation heating with a total irradiation time of one second or less, two-stage irradiation is performed, including a first stage of light irradiation of a semiconductor wafer, which irradiation produces an output waveform that reaches a peak at a given emission output; and a second stage of supplemental light irradiation of the semiconductor wafer, which irradiation is started after the peak, producing an emission output smaller than the above given emission output. The emission output in the second stage is two thirds or less than the above given emission output at the peak. The first-stage light-irradiation time is between 0.1 and 10 milliseconds, and the second-stage light-irradiation time is 5 milliseconds or more. This allows the temperature of the semiconductor wafer even at a somewhat greater depth below the surface to be raised to some extent while allowing the surface temperature to be maintained at a generally constant processing temperature.