The paper presents the results of a study on the characteristics of semiconductor sensors based on thin SnO2 films modified with antimony, dysprosium and silver impurities, with dispersed double Pt/Pd catalysts deposited on the surface to detect carbon monoxide (CO). An original technology has been developed and ceramic targets have been made from powders of the Sn-Sb-O, Sn–Sb-Dy–O, and Sn–Sb-Dy-Ag–O systems synthesized by the sol-gel method. Films of complex composition were obtained by RF magnetron sputtering of the corresponding targets followed by technological annealing at various temperatures. The morphology of films, elemental and chemical composition, electrical and gas-sensitive properties were studied. Special attention is paid to the effect of the film composition on the stability of sensor parameters during long-term tests under the influence of CO. It is shown that a different combination of concentrations of antimony, dysprosium and silver have a significant effect on the size and distribution of nanocrystallites, the porosity and defects of films. The mechanisms of degradation under prolonged exposure to CO are discussed. It has been established that SnO2:0.5 at.% Sb films with optimal crystallite sizes and reduced porosity provide increased stability of carbon monoxide sensor parameters. It has been established that Pt/Pd/SnO2:0.5 at.% Sb films with optimal crystallite sizes and reduced porosity provide the response to the action of 100 ppm carbon monoxide is G1/G0=2–2.5 and increased stability of sensor parameters.