Stability is an important issue for the application of TFTs. In this paper, we present the effects temperature, and humidity on the stability of inverted-staggered back-channel-cut a-Si:H TFTs of various active layer thicknesses. The amorphous TFTs were made at a process temperature of 150°C on 51-μm thick Kapton polyimide foil substrates. With active layer thickness of 50nm, humidity reversibly varies the characteristics of TFTs, but TFTs of active layer thickness greater than 100 nm is pretty stable to the humidity change, which is attributed to backchannel conduction. The temperature dependent stability and characteristics of 200nm active-layer thickness TFTs were analyzed from 20°C to 60°C. Rising temperature from 20°C to 60°C, the threshold voltage (V t ) drops about 2 volts; on-off current ratio decreases by one order of magnitude mainly due to thermally excited carriers .