A method of checking a seal of a probe chamber or test chamber (thermal chamber) during a freezing temperature chamber condition. The thermal chamber provided includes a probe card or a contactor for electrically testing a semiconductor device under test (DUT), a gas inlet, a chiller which provides a freezing chamber temperature, and a pressure sensor for sensing a pressure in the thermal chamber (chamber pressure). Using the pressure sensor, the chamber pressure is sensed while flowing a dry gas through the gas inlet sufficient to render the chamber pressure a positive pressure. The positive pressure is compared to a reference pressure, and from the comparing it is determined whether the thermal chamber is properly sealed.