A series of platinum‐oxygen alloys were grown by sputter deposition using a platinum target and rf‐excited, oxygen‐bearing discharges. The films were deposited on water‐cooled single‐crystal silicon and glass substrates. Optical behavior in the near‐ultraviolet–visible–near‐infrared region was studied by spectrophotometry. Changes in reflection and transmission were correlated with changes in film chemistry and structure. The absorption coefficient and two‐infrared optical transitions across the band gap were determined for a semiconducting Pt‐oxide phase, identified by x‐ray photoelectron spectroscopy as &agr;‐PtO2. These transitions occur at 1.30 eV (0.95 &mgr;m) and 1.47 eV (0.84 &mgr;m).