AbstractHigh‐temperature in situ growth of Ga₂O₃ thin film on flexible substrates for flexible/portable electronic devices is never realized because the conventional polymer substrates cannot meet the thermal‐stability requirements. In the research, for the first time, Ga₂O₃ thin films are directly grown on SiO_x/Al₂O_x buffered Hastelloy substrates. With pulsed laser deposition under high temperature, as‐grown Ga₂O₃ thin films have a fabric texture with a preferred out‐of‐plane orientation along (−201) and a good field‐effect mobility of 18.07 cm² V⁻¹ s⁻¹. The Ga₂O₃ coated tape is patterned with transistor arrays and exhibited good performance homogeneity. The representative transistor devices have a threshold voltage of ≈−2.75 V and a breakdown voltage of 116 V measured under a −20 V gate voltage. Moreover, the tape transistors also have good mechanical robustness. The transistors’ good electrical performance, high uniformity, and mechanical robustness suggest that the in situ deposition technique using Hastelloy tape is promising for fabricating various flexible Ga₂O₃ channeled electronic circuits. Furthermore, it is believed that this technique can be extended to other flexible semiconductor devices that require high‐temperature processing.