We have investigated the total ionizing dose effect by X‐rays, which is a degradation mode of a single transistor, to find the radiation resistance of oxide semiconductor large scale integrated circuit. At 3000 Gy corresponding to the absorbed dose for 30 years in a space environment, or more specifically, on a geostationary orbit, an oxide semiconductor field‐effect transistor showed a negative drift in threshold voltage of less than 300m V and substantially no degradation in subthreshold slope and mobility. After 60 hours from the irradiation, approximately 40% of the threshold voltage variation was recovered.