Abstract: A fast response fluid temperature sensor is disclosed which consists of a silicon temperature sensing semiconductor chip mounted on an extremely thin fin having a high surface area to mass ratio. The fin and chip combination are mounted in a frame assembly, with the thermal conductivity of the frame assembly being high and the specific heat being low for maximum heat transfer from the fluid being sensed to the silicon chip. The chip and fin assembly are illustrated as being open to the free flow of fluid around the assembly, no insulating material being provided between the fluid media being sensed and the fin and chip assembly, and a protective cage is formed around the fin and chip assembly. Suitable connection is made between one electrical terminal of the chip and the fin and between the other electrical terminal of the chip and the external circuitry, with various modified forms of such connections being illustrated.