The conductivity of thin poly crystalline Sn oxide films prepared by spraying solutions of Sn(IV) compounds onto glass or quartz substrates was studied. Conductivity was decreased by increasing the temperature or prolonging the time of heating after hydrolysis, by substituting SnBr4for SnCl4, and by substituting O2for N2during spraying. These effects are explained in terms of nonstoichiometry of the sample and the presence of residual halogens in the crystal lattice as detected by ion‐probe analysi