Plasma damages on the inverted, trilayer a-Si:H thin-film transistor from an n+ RIE process have been detected. These damages include a high threshold voltage, a high off current, and the divergence of the transfer characteristic curves under different drain voltages. Both the bulk of the films and the film-film interfaces were damaged by the plasma. The former was proved by the relation between the threshold voltage shift and the gate dielectric layer thickness and materials. The latter was demonstrated by the plasma radiation exposure experiment. Plasma radiation, instead of the charge buildup on devices, is the major cause of the thin-film transistor's abnormality. All damages were easily repaired with a thermal annealing step.