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 Au111 coated silicon sensors due to chemisorbed alkanethiols is s −0.42 ± 0.0028 N m−1 for 1-dodecanethiol DT and −0.14 ± 0.0028 N m−1 for 1-butanethiol BT. The estimated measurement resolution 1 Hz bandwidth is 0.12 mN m−1 DT: 0.2 pg mm−2 and BT: 0.8 pg mm−2 and as high as 3.82 N m−1 DT: 8 fg mm−2 and BT: 24 fg mm−2 with system optimization. © 2008 American Institute of Physics.