an electric probing - test machine comprises a probe card having a plurality of probes contacted with chips of a semiconductor wafer and serving to apply test signal to a tester which judges whether circuits on the chips of the wafer are correct or deficient , a main chuck for holding the wafer at a test temperature , a system for cooling the main chuck , and a controller for controlling the cooling system . the main chuck includes a chuck top contacted directly with the wafer , a jacket arranged to conduct heat exchange relative to the chuck top , and a temperature sensor for detecting the temperature of the chuck top . the cooling system has a pump for supplying a coolant from a reservoir to the jacket . responsive to temperature information detected by the temperature sensor , the amount of the coolant supplied from the reservoir to the jacket is controlled by the controller to thereby control the temperature of the chuck top .