This paper describes the development and experimental characterization of a wall shear stress sensor system designed to be fully non-invasive to low-speed aerodynamic flows. The differential capacitive microelectromechanical systems (MEMS) sensor is fabricated with backside electrical contacts, eliminating the need for front side wire bonds. Packaged in a modular housing with interchangeable components, the result is a device with less than +/-40 um of deviation over the wetted surface, satisfying the requirements of hydraulic smoothness for low speeds less than 30 m/s. Mean shear stress calibration includes a sensitivity of 38.8 mV/Pa with a +/-0.2% full-scale accuracy for a 50 Pa maximum wall shear stress. Dynamic calibration includes a 3 dB bandwidth of 1.4 kHz with a 45.0 mV/Pa sensitivity and 60 uPa minimum detectable shear stress at 1.128 kHz.