The experiment of the admittance spectroscopy was carried out for the single‐crystal CdS‐Cu2S heterojunction in which the Cu2S was grown chemically on the Cd and S plane of CdS single crystal. The results showed that the concentration of the trapped electrons at the several trapping levels in the depletion layer of the former heterojunction decreases with increasing temperature. The opposite effect, however, was obtained for the latter heterojunction at the temperature below 210 K. The causes for the difference in the heterojunctions will be discussed in this paper.