The values of the activation energy obtained by us indicate the presence of a deep defect level in the band gap, distant by the value of the activation energy from the bottom of the conduction band or from the top of the valence band. Since rs-FeO is characterized by p-type conductivity , we can assume that the defect level is located above the valence band. From the experimental data obtained in the thermal EMF measurements for the two edge compositions (FeO and Fe 0.5 Zn 0.5 O), we can conclude about the p-type conductivity of rock salt Fe 1-x Zn x O solid solutions in the whole range of compositions (0 ≤ x ≤ 0.5).