The invention relates to a material which is pit-gas sensitive at the ambient temperature of 25...30°C, at a pit-gas concentration of 1000 ppm in dry synthetic air, and to a process for preparing the same, the claimed material being applicable in the field of medicine, environment protection, mining industry, food industry and the like. According to the invention, the material is a thin film consisting of a mixture of equal parts of a base material made of SnSeand an addition material (Zn(II)-5, 10, 15, 20-tetrakis-(4-amino phenyl)-porphyrin). The process, as claimed by the invention, consists in dissolving SnSepowders as a base material and an addition material (Zn(II)-5, 10, 15, 20-tetrakis-(4-amino phenyl)-porphyrin) in specific amine- and methyl-based solvents, in concentrations of 10...10mole/l, to result in two solutions which are mixed by ultrasonication, an amount of 30 μ l from the mixture solution being deposited by drop casting, on interdigitated electrode structure, the so-formed deposit being then dried to remove the solvent, in an oven, under continuous flow of protective argon atmosphere, at a constant pressure of 1.2 at, at temperatures in the range of 70...250°C, for a period of 60...100 min, where, after drying the drop-cast deposit, a grey even thin film covering completely the sensor-support electrodes is obtained, followed by electrical contacting of the terminations of interdigitated electrodes for introducing the sensor into the gas-testing enclosure.