Gate-all-around (GAA) nanosheet field-effect transistors (FETs) based on 2D semiconductors hold promise to complement silicon in future integrated circuits. Here, the authors report the wafer-scale growth of high-κ dielectric/semiconductor β-Bi2SeO5/Bi2O2Se/α-Bi2SeO5 heterostructures and their application for high performance 2D GAA FETs.