Polysilicon N-channel TFT have been hydrogenated using the H2 dissociation on a hot tungsten filament. A post-annealing realized at the optimal temperature of 300°C is necessary to obtain interesting electrical TFT characteristics. Different TFT's sizes and geometries have been processed. The analysis of their characteristics shows that hydrogen preferentially diffuses through silicon oxide layer. The enhancement of the current in the ON-state shows that hydrogen atoms have passivated silicon oxide gate / polysilicon interface traps. The important reduction of the dependency of the OFF-state current with the reverse gate voltage shows that hydrogen atoms have passivated grain boundary traps near the interface in the channel region and in the drain sheet resistance region then reducing the trapped carrier emission.