This study demonstrates the successful epitaxial growth of 2-inch single-crystal MoS₂ monolayers on industry-compatible c-plane sapphire substrates by controlling the S/MoO₃ precursor ratio. The unidirectional alignment and seamless stitching of MoS₂ domains across the entire wafer are achieved through multi-scale characterizations, ranging from atomic to centimeter scales. The resulting monolayer MoS₂ single crystals exhibit high wafer-scale uniformity and state-of-the-art quality, as evidenced by excellent phonon circular dichroism, exciton valley polarization, room-temperature mobility, and on/off ratio. This work provides a simple strategy for producing wafer-scale single-crystal 2D semiconductors on commercial insulator substrates, paving the way for the extension of Moore's law and industrial applications of 2D electronic circuits.This study demonstrates the successful epitaxial growth of 2-inch single-crystal MoS₂ monolayers on industry-compatible c-plane sapphire substrates by controlling the S/MoO₃ precursor ratio. The unidirectional alignment and seamless stitching of MoS₂ domains across the entire wafer are achieved through multi-scale characterizations, ranging from atomic to centimeter scales. The resulting monolayer MoS₂ single crystals exhibit high wafer-scale uniformity and state-of-the-art quality, as evidenced by excellent phonon circular dichroism, exciton valley polarization, room-temperature mobility, and on/off ratio. This work provides a simple strategy for producing wafer-scale single-crystal 2D semiconductors on commercial insulator substrates, paving the way for the extension of Moore's law and industrial applications of 2D electronic circuits.