<p>To drive next-generation high-resolution and high-refresh-rate displays, transistors with high mobility exceeding 40 cm²/V·s are essential. Although amorphous Indium Gallium Zinc Oxide (a-IGZO) thin-film transistors (TFTs) are key components of next-generation displays, their conventional mobility of approximately 10–20 cm²/V·s limits their application in these advanced displays and presents a fundamental trade-off between mobility and stability. Increasing the Indium content to enhance mobility leads to higher carrier concentration, causing the threshold voltage to shift negatively and significantly degrading stability under bias stress. Heterojunction channel structures have been investigated as a strategy to address these issues. The heterojunction structure decouples the functions of the high-mobility layer and the stability control layer. It is reported that a high electron density accumulation layer, known as a Two-Dimensional Electron Gas like layer (2DEG-like layer), can be formed at the interface, contributing to mobility enhancement. This improves the transistor mobility to over 40 cm²/V·s. Furthermore, precise conduction band offset engineering forms an energy barrier that suppresses electron trapping, thereby improving bias stability. This review comprehensively analyzes the 2DEG induction mechanism in IGZO-based heterojunction TFTs, the control of bandgap engineering, and the performance of key material systems such as ITO/IGZO and IZO/IGZO.</p>