Here,　the　bilayer　InGaZnO/In2O3　thin-film　transistors　(TFTs)　are　deposited　by　radio-frequency　magnetron　sputtering　at　room　temperature.　A　high　field-effect　mobility　(mu(FE))　of　64.4　cm(2)　V-1　s(-1)　and　a　small　subthreshold　swing　(SS)　of　204　mV　per　decade　are　achieved　in　the　bilayer-stack　TFTs　fabricated　upon　SiO2/Si　substrate,　with　large　improvement　compared　to　the　single-layer　InGaZnO　and　In2O3　TFTs.　Implementing　HfO2　and　Si3N4　as　high-k　gate　dielectrics,　mu(FE)　and　SS　are　correspondingly　enhanced　to　be　67.5　and　79.1　cm(2)　V-1　s(-1),　and　85　and　92　mV　per　decade　in　the　bilayer　TFTs.　Defect　self-compensation　effect　is　also　revealed,　i.e.,　(In)(+)　+　(O)(-)　-＞　In-O,　while,　respectively,　considering　the　indium-　and　oxygen-related　defects　in　InGaZnO　and　In2O3　and　exploring　the　numerical　simulations　in　SILVACO/Atlas　(for　electrical　performance)　and　Quantum　Espresso　(for　physical　analysis).　The　In-O　formation　can　result　in　a　significant　reduction　in　defect　density　(validated　by　the　X-ray　photoelectron　spectra　and　low-frequency　noise　characterizations)　and　therefore　improvement　of　mu(FE)　and　SS　in　the　bilayer-stack　TFT.　The　important　role　of　defect　self-compensation　mechanism　while　combining　different　individual　channel　layers　in　the　oxide　semiconducting　TFTs　is　underlined　and　highly　potential　application　in　next-generation,　fast-speed　flexible　displays　is　shown.