In this study, we investigated the impact of Ti content on structural properties and electrical characteristics of high-k Yb₂TiO₅ gate dielectrics for amorphous indium–zinc–tin-oxide (a-InZnSnO) thin-film transistor (TFT) devices. The Yb₂TiO₅ thin films with different Ti plasma conditions were integrated in metal-insulator-metal structures to check the electrical capabilities. The Yb₂TiO₅ a-InZnSnO TFT device fabricated at the 120 W condition exhibited excellent electrical characteristics in terms of a small threshold voltage (V_TH) of 0.14 V, a low subthreshold swing of 202 mV/decade, a large field-effect mobility of 29.8 cm²/V-s, and a high I_on/I_off current ratio of 2.7×10⁸. In addition, the V_TH stability of Yb₂TiO₅ a-InZnSnO TFT device was studied under both positive bias stress and negative bias stress conditions. The Yb₂TiO₅ thin film is a promising gate dielectric material for the fabrication of a-InZnSnO TFTs.