This paper has aimed at creating a more complete picture about the instability mechanism responsible for a-Si:H/SiN TFTs degradation. Additional insight about the degradation kinetics in a-Si:H/SiN TFTs is obtained by the in-situ monitoring of the source to drain current during alternative periods of stress and relaxation. The results presented in this paper come to the conclusion that the physical mechanism responsible for instability of the device operating at low bias stress, short stress time and different temperatures is a combination of defect creation and the trapping/detrapping of the carriers.