An electrochemical resistive-type sensor device, with a mesoporous silica thin film as sensitive membrane, has been developed and characterised. The silica film has been obtained via evaporation-induced self-assembly (EISA) using a tri-block copolymer (Pluronic F-127) as templating agent. It has been deposited by dip-coating on a silicon substrate with metallic interdigitated electrodes. Fast, reversible and reproducible electrical responses to relative humidity changes have been observed for the sensor device. The conduction mechanism has been related to chemical properties, structural order and surface morphology of the porosity in the silica film, confirming the dependence on the film preparation method and overall the importance of calcination temperature.