Abstract <p>Sensors based on mixed metal-oxide semiconductors are characterized by their fast response and low power consumption. Zinc oxide is widely used as a binary compound in these sensors. Gas-sensitive structures based on ZnO can be improved by creating nearby adsorption sites for the sensitizer gas and the detected gas. In this study, gas-sensitive layers based on zinc oxide nanorods are obtained by a hydrothermal method and then modified in solutions containing potassium stannate and iron sulfate as precursors to form ZnO–Sn and ZnO–Fe composite samples, respectively. Using X-ray photoelectron spectroscopy, the effect of the modification of sensor layers consisting of zinc oxide nanorods with subsequent treatment in solutions of compounds of other metals (tin and iron) on the chemical composition of the surface is analyzed. The sensor properties of the obtained samples are analyzed when detecting isopropyl alcohol vapors. It is found that depending on the technological conditions, the oxygen content in the form of adsorbed particles changes. Oxygen vacancies participate in the adsorption of these particles. It is shown that the gas-sensitive properties depend on the content of oxygen vacancies. It is established that the sensor layers are modified in the process of formation of ZnO–Sn and ZnO–Fe composite surface structures and leads to changes in the distribution of adsorption sites and their energy. The active oxygen and reducing gas adsorption sites are transformed with a change in the concentration of oxygen vacancies and leads to an increase in the sensor response to isopropyl alcohol vapor.</p>