The stability of p-channel polycrystalline silicon thin-film transistors, hydrogenated in pure hydrogen plasma, is investigated. The hot-carrier induced degradation mechanisms are studied for operation in the saturation region and different gate bias voltages V-g. During on-state stress at high \V-g\, first an effective shortening of the channel length is observed due to trapping of hot electrons. As the stress proceeds further, donor-type interface states are generated, resulting in an increase of the electric field near the drain due to built-up of positive charge in these states by trapping of hot holes. During on-state stress at low \V-g\, the transistor parameters are improved due to further passivation of grain boundary deep and tail states, caused by dissociation of hydrogen molecules by hot electrons near the drain region. During off-state stress, hot electrons are injected in the gate oxide near the drain causing an effective shortening of the channel length and a reduction of the minimum leakage current. (C) 2002 Elsevier Science Ltd. All rights reserved.