In this work, we present an optical sensor for quantitative determination of the alcohol content in hydro-alcohol mixtures, realized by using porous silicon (PSi) nanotechnology. The device is an oxidized PSi micro-cavity (PSMC) constituted by a Fabry–Perot layer between two distributed Bragg reflectors. Due to the capillary condensation, a red shift of the PSMC reflectivity spectrum is observed on exposure to vapour mixtures. The phenomenon is completely reversible. Moreover, to reduce the analysis time, we have designed the integration of the sensor in a thermally controlled lab-on-chip, by merging PSi and anodic bonding technologies. Numerical calculations have been performed to study the thermal behaviour of the integrated device.