A sensor assembly that responds to temperature of fluids within an annulus formed by an outer surface of a borehole instrument and the wall of a borehole. The sensor assembly is removably installed preferably in the wall of the borehole instrument. Installation and removal are from outside of the borehole instrument thus eliminating the need to disassemble the borehole instrument. The sensor assembly comprises a temperature transducer that is hermetically sealed within a housing designed to obtain maximum thermal exposure of the transducer. Power to the temperature transducer is supplied from a separate electronics package in the borehole instrument through a rotary connector within the sensor housing.