We studied the variations of electrical characteristics induced by bias stress on low-temperature polycrystalline silicon (LTPS) p-channel thin film transistors (TFTs) fabricated on metal foil. The transfer characteristics resulted quite stable upon application of prolonged bias stress, whereas the output characteristics presented a reduction of kink-effect. These results have been explained by using a self-consistent model based on the trapping of hot electrons, generated by impact ionisation and injected near drain contact, at both front (gate oxide/channel) and back (substrate/channel) interfaces.