A hydrogen sulfide sensor is made from a metal acetate film, such as a thin film of copper acetate, formed on a set of monitoring electrodes, by evaporation of a metal acetate aqueous solution disposed on the electrodes, for detecting a weak gas, such as hydrogen sulfide, carried in a gas carrier, such as a nitrogen carrier, for detecting low concentration of the weak gas, such as ten ppm, when the conductivity of the film changes by several orders of magnitude, that produces a metal sulfide, such as copper sulfide, that is a good electrical conductor at room temperature, for example, as the metal acetate is converted directly to a metal sulfide upon exposure to hydrogen sulfide.