The thermal oxidation of silicon at lower temperature by using dinitrogen monoxide (N₂O) gas and UV-irradiation has been investigated. A low pressure mercury lamp is used as light source. Silicon can be oxidized thermally at 300°C. The main oxidizing species are the atomic oxygen O(¹D) which is created by the dissociation of N₂O during UV-irradiation. Oxide thickness is 4.7 nm at 500°C for 4h oxidation. It is clear from AES analysis that the composition of silicon and oxygen atom in the film formed by the present technique is same as that formed by high temperature oxidation in common dryO₂ ambient. High frequency C-V characteristics for the film in the present technique is better than that in common dryO₂ oxidation.