Abstract: An intermetallic thermal sensor comprised of a hermetically sealed housing containing alternating layers of electronegative and active metals or their alloys in intimate contact. The layers may be wafer or washer-shaped. If washer-shaped, the holes in the wafers are aligned with each other to create a well within the housing and any extension thereof. A tubular-shaped liner extends into the well and may contain an energetic composition such as BKNO.sub.3. In one embodiment a thermite charge in the sensor can be ignited for venting applications. The active metal and electronegative metal and their alloys are selected so that when the melting point of one or both metals, alloys, or metal and alloy pairs has reached its or their melting point in response to external heat within a design range of the sensor, a vigorous exothermic reaction occurs to initiate a gas-producing reaction in the well or to ignite the thermite for operation of a cook-off mitigation system.