PURPOSE: To inhibit the large fluctuation of an ashing rate due to a temperature change in a chamber, and to stabilize treatment in the chamber by installing a temperature sensor measuring the temperature of the treating chamber, in which a work is mounted into a vacuum chamber, and a means controlling the degree of vacuum, the flow rate of a treating gas or high-frequency power so as to keep the treatment of the work constant with an output from the temperature sensor.

CONSTITUTION: A treating gas is introduced through a gas flow controller 3 into a quartz chamber 1 evacuated by a vacuum pump 4 and held by upper and lower electrodes 2a, 2b, and power is applied to the upper and lower electrodes 2a, 2b from a high-frequency power 5a, thus starting the treatment of the surfaces of semiconductor substrates 6. A temperature during treatment is measured by a temperature sensor 7 after the start of the treatment, the signal of the temperature is transmitted to the high-frequency power 5a by a thermometer and a temperature output device 8, and high-frequency power is controlled in conformity with the signal.