Abstract: A temperature sensing apparatus particularly adapted for use in a rarefied fluid media has a sensing device including a small spreading resistance type of resistor element formed of a semiconducting material of positive temperature coefficient of resistivity. Leads connect the element in a circuit; the element is encapsulated; and a vane of high thermal conductivity is secured in heat-transfer relation to the element to extend outside the encapsulating material for conducting heat to the element from a temperature zone to be monitored. The apparatus includes mounting apparatus having a plurality of housing sections of low thermal conductivity which are secured together to hold the sensing device therebetween. The housing sections hold the sensing device so that the vane is exposed in the temperature zone and the housing sections have extensions disposed in spaced surrounding relation to the vane for physically protecting the vane while permitting fluid to flow over the vane.