The effects of synchrotron radiation (SR) irradiation on molybdenum oxide are studied. Removal of native molybdenum oxide by SR irradiation is observed by reflection high-energy electron diffraction and Auger-electron spectroscopy measurements. SR irradiation changes MoO3 thin films to MoO2. Indications are that SR-stimulated oxygen desorption is the cause. Those SR-irradiated molybdenum surfaces which are originally covered with native oxide are found to be highly reactive with disilane gas, while nonirradiated surfaces are not.