A thermometric apparatus for determining a patient's temperature having a elongated sensing probe that is connected to a base housing. The insertion tip of the probe contains a outer shell and a spaced apart inner shell. The outer surface of the inner shell has a heater that is fabricated of a resistive thick film material and a heat sensor mounted thereon. The heater and the heat sensor are connected to a pair of thick film conductive traces which in turn are electrically attached by a flexible circuit board to leads running back to the base housing. The space between the two shells is filled by a thermally conductive epoxy.