Low-temperature polysilicon(LTPS) thin-filmtransistors (TFTs) have recently been applied as driving transistors in active-matrix organic light-emitting displays (AMOLEDs)[1, 2]. This application requires very reliable devices and p-channel LTPS TFTs are often preferred, as they are less influenced by hot carrier effects than n-channel TFTs [3, 4]. However, the p-channel devices show degradation of the electrical characteristics when operated at high temperatures and/or at high gate and drain voltages because so that the dissipated power is large enough to induce appreciable self-heating in the device [5]. The instabilities observed in p-channel TFTs have been related to a negative bias-temperature instability (NBTI) effect [6, 7], commonly observed in crystalline silicon p-channel metal-oxide-semiconductor field-effect transistors (p-MOSFET)[8–10]. NBTI in p-MOSFETs has been widely investigated (see Refs. 8 and 9 for reviews) and has been attributed to the generation of a broad interface peak of donor states in the lower half of the gap and an approximately equal amount of positive trapped charge [11].