The controlled synthesis of large-area, high-quality two-dimensional (2D) MoS2 single crystals from a single nucleus is essential for applying this ultrathin semiconductor to next-generation integrated circuits to extend Moore’s law. However, the complexity of traditional synthesis reactions hinders the reproducibility and controllability required for practical implementation. Here, we simplify the synthesis reactions by employing a distinctive all-in-one K2MoS4 precursor. Through thermal decomposition, this precursor simultaneously provides Mo and S sources, a growth promoter, and a protector, a mechanism confirmed by comprehensive theoretical calculations, in situ X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The single-crystal domain size of the obtained monolayer MoS2 derived from a single nucleus reaches up to 6 mm, exceeding that of other gas-phase synthesized samples. Furthermore, these large monolayer samples exhibit high crystallinity and uniformity, with room-temperature carrier mobilities as high as ∼105 cm2 V–1 s–1. Our study underscores the critical role of chemical reaction design in synthesizing large-scale 2D semiconductors, paving the way for their application in scalable next-generation electronics.

J. Am. Chem. Soc. 2026, https://doi.org/10.1021/jacs.6c02743