Capacitive measurement of very small displacement of nano-electro-mechanical systems (NEMS) presents some issues that are discussed in this article. It is shown that performance is fairly improved when integrating on a same die the NEMS and CMOS electronics. As an initial step toward full integration, an in-plane suspended gate MOSFET (SGMOSFET) compatible with a front-end CMOS has been developed. The device model, its fabrication, and its experimental measurement are presented. Performance obtained with this device is experimentally compared to the one obtained with a stand-alone NEMS readout circuit, which is used as a reference detection system. The 130 nm CMOS ASIC uses a bridge measurement technique and a high sensitive first stage to minimize the influence of any parasitic capacitances.