In an exemplary embodiment, a temperature sensor and a 4-20 mA transmitter on a single flexible circuit subassembly with a separate housing suitable for use in industrial control or HVAC applications. In a preferred embodiment, a narrow flex circuit substrate includes a silicon diode-based surface-mount sensor at a sensor end, a surface-mount programmable transmitter IC on a flex circuit substrate in the transmitter section, conductive traces connecting the sensor to the transmitter IC, and two conductive pads at an output end for connecting the 4-20 mA output to a pair of external wires. Additional traces on the flex subassembly are provided for testing and programming the transmitter IC and sensor. The sensor end of the flex subassembly is mounted in a metal sensor tube, filled and sealed in the same manner as RTD or thermistor sensors with leads are currently assembled for use in industrial control or HVAC applications.