Evidence for direct application of the chalcogenide semiconductors for gas sensing is considered, Two kinds of sensitive thin film structures have been fabricated and studied, using both artificial dimorphite (As₄S ₃) and As-Ge-Te alloys. The As₄S₃ thin films are porous with fibrillar morphology but the tellurium based films were polycrystalline. Resistive gas sensitive devices based on these chalcogenide films have been checked in media with nitrogen dioxide and propylamine (C ₃H₇NH₂), The results are discussed in terms of the vapour - solid interaction that means the chemisorption of gas molecules and their trapping at charged centres. The gas-induced response is found to be high, fast and with a good reproducibility. The applications for environmental monitoring and process control are considered.