When exposed to air, YBa2Cu3O7−xreacts to form a nonsuperconducting surface layer which degrades the quality of devices formed by subsequent deposition of overlayers. Degradation may also be caused by contamination of the surface during prior processing. We have investigated the use of thermal oxidation treatments as a means of restoring these surfaces,in situ, prior to overlayer deposition. The oxidations were performed in a dual chamber UHV system equipped with x‐ray and ultraviolet photoelectron spectroscopies, ion scattering spectroscopy, and a four point probe forin situresistance measurements. Sputter‐deposited, annealed YBa2Cu3O7−xthin films exposed to air underwent treatments at 350–650 °C for 5–60 min in 10–300 Torr of oxygen. Carbonate contamination was removed at T≥460 °C. Chlorine contamination present on some samples was removed at T≥600 °C. Resistance measurements indicate that the oxygen content within the films can be maintained during these treatments if a suitable temperature profile is used. The resulting surfaces are not ideal—an insulating layer ∼1 nm thick and deficient in yttrium is present. Nevertheless, the treatments described here may prove to be useful steps in device fabrication.