The capacitance spectra of the interdigital Pt–glassy As2Te13Ge8S3–Pt structures have been investigated in a range of 5–106 Hz with respect to temperature effects in both dry air and its mixture with a controlled concentration of nitrogen dioxide. It has been found that a decrease in the frequency of applied voltage to 103 Hz results in a rapid increase in the capacitance by several orders of magnitude. Environmental conditions dramatically influence the capacitance at low frequencies and, together with temperature regime, control the capacitance spectra and current–voltage characteristics of the films. The results are explained in terms of formation of a Schottky–Mott barrier that controls the properties of the contact junction. The contact-free part of the chalcogenide film surface, being more conducting than the bulk, acts as a capacitor, which can be controlled by interaction with gaseous species from the environment.