The experimental and analytical results regarding to the effects of temperature and electrical stress on the characteristics of amorphous silicon thin-film transistors (a-Si TFT's) have been presented. The variations in the device parameters of a-Si TFT, such as threshold voltage and field-effect mobility, have been examined under various operating temperatures and electrical stress conditions. The hysteresis in the transfer characteristics and the trapped charges at the a-Si/silicon nitride interface were measured at the operating temperature ranges. From the experimental results, it has been found out that the increase of the interface charge trapping may be responsible for the degradation in the a-Si TFT characteristics. Also, an analytical formulation, employing the interface charge trapping, is presented to clarify the instability phenomena and verified successfully with the experimental results.