A micromachined surface stress sensor has been fabricated and integrated off chip with a low-noise, differential capacitance, electronic readout circuit. The differential capacitance signal is modulated with a high frequency carrier signal, and the output signal is synchronously demodulated and filtered resulting in a dc output voltage proportional to the change in differential surface stress. The differential surface stress change of the Au(111) coated silicon sensors due to chemisorbed alkanethiols is Deltasigma(s) approximately -0.42+/-0.0028 N m(-1) for 1-dodecanethiol (DT) and Deltasigma(s) approximately -0.14+/-0.0028 N m(-1) for 1-butanethiol (BT). The estimated measurement resolution (1 Hz bandwidth) is approximately 0.12 mN m(-1) (DT: 0.2 pg mm(-2) and BT: 0.8 pg mm(-2)) and as high as approximately 3.82 microN m(-1) (DT: 8 fg mm(-2) and BT: 24 fg mm(-2)) with system optimization.