It was investigated the temperature dependence of the specific resistivity and thermoe-lectric power of (AgSbTe2)0.8(PbTe)0.2 in the 80-550 K temperature range and the spec-troscopic ellipsometric optical measurements at 300K. The band gap of (AgS-bTe2)0.8(PbTe)0.2 was estimated according to experimental data on electrical conductivity (Еg=0.13eV), thermal power (Еg=0.18eV) and using Vegard's rule (Eg=0.214 eV). The val-ue Еg=0.2eV for band gap of (AgSbTe2)0.8(PbTe)0.2) was obtained according to optical measurements.