Use: detecting the presence of small concentrations of target gases. A method for selectively determining the concentration of gaseous mercaptan-containing and/or amino-containing compounds using a gas sensor based on an organic field-effect transistor is characterized in that the magnitude of a current in the channel of an organic field-effect transistor is measured in a time-dependent manner; the magnitude of a threshold opening voltage of the organic field-effect transistor and the magnitude of the charge carrier mobility are calculated in a time-dependent manner on the basis of the data regarding the time-dependent magnitude of the current in the channel of the organic field-effect transistor; the magnitude of the relative change in charge carrier mobility and the magnitude of the shift in the threshold opening voltage of the organic field-effect transistor are calculated; a detectable mercaptan-containing and/or amino-containing compound is determined according to the value of the magnitudes of the relative change in charge carrier mobility and of the shift in the threshold opening voltage of the organic field-effect transistor; the concentration of the detectable mercaptan-containing compound is determined according to the magnitude of the relative change in charge carrier mobility, and/or the concentration of the detectable amino-containing compound is determined according to the shift in the threshold opening voltage of the organic field-effect transistor. Technical result: creation of a device for the independent selective measurement of small concentrations (from 10 ppb to 1 ppm) of mercaptan-containing and/or amino-containing compounds in atmospheric air or in gas mixtures.