We investigated the temperature-dependent stability on the inverted-staggered back-channel-etched a -Si : H thin film transistors (TFTs) made at a process temperature of 150 ° C on plastic foil substrates. The shift of threshold voltage (ΔV_t) increases with the stressing time and the stressing temperature. Different from TFTs made at temperatures of 300 ° C or above, our low-temperature processed TFTs show an abnormal saturation of ΔV_t at 50 ° C (323 K) in a constant gate-bias stress experiment. Around the same temperature, we observed abrupt increases in both the gate leakage current and the off current. Because of the low process temperature, the gate dielectric is less stable and more defective compared to that made at high process temperatures. A substantial amount of charges, trapped inside the dielectric during TFT fabrication and gate-bias stressing, was thermionically emitted into the channel by the Poole–Frenkel emission mechanism at a stressing temperature of 50 ° C , leading to the abnormal phenomena.