The effect of 5 MeV high-energy proton irradiation on solution-processed metal-oxide thin-film transistors (TFTs) is investigated. The electrical characteristics of the devices are measured before and after proton irradiation with radiation doses of 10 13 , 10 14 , and 10 15 cm −2 . TFTs based on zinc oxide (ZnO) and amorphous indium gallium zinc oxide (a-IGZO) exhibit a significant negative shift in their threshold voltage values (ΔV th ≤ −30 V) or transitioned to the conductor state as the proton radiation dose increased. For a-ZnO and IGZO, this change in the electrical characteristics originates from the formation of proton-irradiation-induced oxygen vacancies in the metaloxide semiconductor layer. On the other hand, amorphous zinc tin oxide devices with an optimized composition exhibit relatively stable electrical characteristics when subjected to proton irradiation. Furthermore, the backchannel passivation of oxide-semiconductor TFTs with an n-type organic semiconductor layer significantly improves the device stability under proton irradiation. This study demonstrates that solution-processed metal-oxide semiconductors have significant potential as rad-hard large area electronic devices for nuclear and aerospace applications.