Hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) have been prepared using PECVD SiO2, deposited under different deposition conditions, as the dielectric. The layers were evaluated to determine the best deposition regime with regard to the index of refraction and electrical insulation properties. This regime was found to be a deposition temperature of 200 degrees C, rf power density of 145 mW cm(-2), and a flow rate ratio of O-2 to a 10 vol.% mixture of SiH4 in H-2 in the interval 7-25. The devices were characterized by measuring the effective mobility, the threshold voltage, and their behavior in the sub-threshold regime. The influence of low-temperature annealing on these parameters was determined. The best results were obtained when the devices were annealed in the temperature interval 250-300 degrees C.