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Metal-oxide thin-film transistors (TFTs) have been developed as promising candidates for use in various electronic and optoelectronic applications. In this study, we fabricated bilayer zinc oxide (ZnO)/indium oxide (In₂O₃) TFTs by using the sol-gel solution process, and investigated the structural and chemical properties of the bilayer ZnO/In₂O₃ semiconductor and the electrical properties of these transistors. The thermogravimetric analysis results showed that ZnO and In₂O₃ films can be produced by the thermal annealing process at 350 °C. The grazing incidence X-ray diffraction patterns and X-ray photoemission spectroscopy results revealed that the intensity and position of characteristic peaks related to In₂O₃ in the bilayer structure were not affected by the underlying ZnO film. On the other hand, the electrical properties, such as drain current, threshold voltage, and field-effect mobility of the bilayer ZnO/In₂O₃ TFTs obviously improved, compared with those of the single-layer In₂O₃ TFTs. Considering the energy bands of ZnO and In₂O₃, the enhancement in the TFT performance is explained through the electron transport between ZnO and In₂O₃ and the formation of an internal electric field in the bilayer structure. In the negative gate-bias stress experiments, it was found that the internal electric field contributes to the electrical stability of the bilayer ZnO/In₂O₃ TFT by reducing the negative gate-bias-induced field and suppressing the trapping of holes in the TFT channel. Consequently, we suggest that the bilayer structure of solution-processed metal-oxide semiconductors is a viable means of enhancing the TFT performance.