An oxide phase which is isostructural with PdO has been obtained as a thin film by reactive dc diode sputtering of Pt in argon‐oxygen mixtures. Films in which this is the only crystalline phase observed have been prepared; they have a density of 13.5±1.0 g/cm3. The oxide phase is unstable at temperatures above 500 °C, and the film is converted to platinum. Thermogravimetric analysis of the films indicates that the original composition is close to PtO. Mixtures of PtO and Pt can also be obtained and the temperature coefficient of resistance of the films becomes more negative with increasing PtO content; values between +1800 and −25 000 ppm/°C have been measured.