Temperature dependence of the electrical conductivity of CuInS 2 –ZnIn 2 S 4 and CuInSe 2 –ZnIn 2 Se 4 solid solutions possessing n-type conductivity has been studied. It has been established that when the temperature decreases down to ~100 to 27K, the hopping mechanism of electrical conductivity with a variable jumping length between localized states positioned in a narrow energy band near the Fermi level becomes dominant. The main parameters of the hopping conductivity have been determined. At higher temperatures (150–300K), in the CuInSe 2 –ZnIn 2 Se 4 single crystals containing 15 and 20mol% ZnIn 2 Se 4 the thermally activated conductivity with activation energy of 0.018 and 0.04eV, respectively, is detected. Among the CuInSe 2 –ZnIn 2 Se 4 single crystals, samples with 5 and 10mol% ZnIn 2 Se 4 were found to be close to degenerate semiconductors. Temperature dependences of the electrical conductivity of CuInS 2 –ZnIn 2 S 4 single crystals are described by a more complicated function that may indicate a competition of several conduction mechanisms in these compounds. For the CuInS 2 –ZnIn 2 S 4 solid solutions, X-ray photoelectron core-level and valence-band spectra have been measured for both pristine and Ar + ion-bombarded surfaces. Our results indicate that the Cu 1−x Zn x InS 2 single-crystal surfaces are sensitive to Ar + ion-bombardment. Additionally, for the Cu 1−x Zn x InS 2 crystal with the highest ZnIn 2 S 4 content, namely 12mol% ZnIn 2 S 4 , the X-ray emission bands representing the energy distribution of the Cu 3d, Zn 3d and S 3p states have been measured and compared on a common energy scale with the X-ray photoelectron valence-band spectrum.