Thin amorphous Ge–S–AgI films were thermally evaporated on cantilever sensors and their sorption properties were investigated upon exposure to volatile analytes, such as water, ethanol, acetone, and ammonia vapours. The films were smooth and uniform in thickness as revealed by atomic force and scanning electron microscopies. The exposure to the analytes resulted in a change of the resonance frequency of the cantilever. Initially, the largest dynamic responses (frequency shifts) were observed towards acetone, i.e. the cantilever acted as a resonant microbalance. When the sensor was exposed to ammonia, its molecules were chemisorbed on the surface of the sensitive layer. This surface modification increased the sensor sensitivity towards water molecules by the creation of new interaction sites.