PURPOSE: To enable the sensitivity of the sensor to be sufficiently increased even if the sensor structure is miniaturized by a method wherein a p type polycrystalline silicon resistor and an n type polycrystalline silicon resistor are alternately series-connected to constitute a thermopile.

CONSTITUTION: p type and n type polycrystalline resistors 15, 16 are respectively formed of p type polycrystalline silicon film 17 and an n type polycrystalline silicon film 18 covered with a silicon oxide film 19. At this time, mutually adjacent p type polycrystalline silicon resistor 15 and the n type polycrystalline silicon resistor 16 are series-connected by metallic wires 20 to constitute a thermopile. Accordingly, an infrared beam absorbing film 14 is aerially supported above a dent part 12 only by beamlike plural p type and n type polycrystalline silicon resistors 15, 16. Through these procedures, the heat resistance of a thermal detector can be stiffened thereby enabling the sensitivity of the sensor to be increased when the sensor is miniaturized.