Oxide semiconductors have been extensively studied as active channel layers of thin-film transistors (TFTs) for electronic applications. However, the field-effect mobility (μ_FE) of oxide TFTs is not sufficiently high to compete with that of low-temperature-processed polycrystalline-Si TFTs (50–100 cm²V⁻¹s⁻¹). Here, we propose a simple process to obtain high-performance TFTs, namely hydrogenated polycrystalline In₂O₃ (In₂O₃:H) TFTs grown via the low-temperature solid-phase crystallization (SPC) process. In₂O₃:H TFTs fabricated at 300 °C exhibit superior switching properties with µ_FE = 139.2 cm²V⁻¹s⁻¹. The hydrogen introduced during sputter deposition plays an important role in enlarging the grain size and decreasing the subgap defects in SPC-prepared In₂O₃:H. The proposed method does not require any additional expensive equipment and/or change in the conventional oxide TFT fabrication process. We believe these SPC-grown In₂O₃:H TFTs have a great potential for use in future electronic applications.