This paper describes the use of an inexpensive, ubiquitously available, silicon pnjunction diode, the 1N4148, in the design of a very accurate thermometer for use in a teaching laboratory. The operational theory is based on the fact that if the forward bias current through a pnjunction diode is fixed, the barrier potential of the diode has a linear temperature coefficient. The diode thermometer is compared against standard sensor and is found to be very accurate.
