The　intriguing　properties　of　zinc　oxide-based　semiconductors　are　being　extensively　studied　as　they　are　attractive　alternatives　to　current　silicon-based　semiconductors　for　applications　in　transparent　and　flexible　electronics.　Although　they　have　promising　properties,　significant　improvements　on　performance　and　electrical　reliability　of　ZnO-based　thin　film　transistors　(TFTs)　should　be　achieved　before　they　can　be　applied　widely　in　practical　applications.　This　work　demonstrates　a　rational　and　elegant　design　of　TFT,　composed　of　poly　crystalline　ZnO:H/ZnO　bilayer　structure　without　using　other　metal　elements　for　doping.　The　field-effect　mobility　and　gate　bias　stability　of　the　bilayer　structured　devices　have　been　improved.　In　this　device　structure,　the　hydrogenated　ultrathin　ZnO:H　active　layer　(similar　to　3　nm)　could　provide　suitable　carrier　concentration　and　decrease　the　interface　trap　density,　while　thick　pure-ZnO　layer　could　control　channel　conductance.　Based　on　this　novel　structure,　a　high　field-effect　mobility　of　42.6　cm(2)　V-1　s(-1),　a　high　on/off　current　ratio　of　108　and　a　small　subthreshold　swing　of　0.13　V　dec(-1)　have　been　achieved.　Additionally,　the　bias　stress　stability　of　the　bilayer　structured　devices　is　enhanced　compared　to　the　simple　single　channel　layer　ZnO　device.　These　results　suggest　that　the　bilayer　ZnO:H/ZnO　TFTs　have　a　great　potential　for　low-cost　thin-film　electronics.