Abstract: A novel method for preparation of a dense diffusion barrier limiting current oxygen sensor is presented. The dense thin‐layer with the nominal composition Sr‐, Mg‐ and Fe‐doped lanthanum gallate (LSGMF) was prepared over La0.8Sr0.2Ga0.8Mg0.2O3–δ (LSGM) electrolyte by a thermal diffusion method. The crystal structure, morphology, elemental distribution, conductivity, and sensing performance of the prepared sample were investigated. X‐ray diffraction (XRD) analysis shows a highly crystalline perovskite. SEM‐EDS analysis shows that the dense thin‐layer with about 40 μm thickness is well attached to the solid electrolyte. Electrical conductivity measurement shows that the dense thin‐layer has high conductivity of 8.73 S·cm−1 at 800°C. The oxygen sensor exhibits good sensing performance. The variations of the limiting current (IL) vs oxygen content (x(O2)) can be obtained as follows: I L ( mA ) = 96.65 x ( O ) 2 ( mol ) % + 28.62 [ABSTRACT FROM AUTHOR]