<p>Two-dimensional (2D) transition-metal dichalcogenide (TMDC) heterostructures are promising for next-generation optoelectronics, yet the mechanisms controlling their vertical heteroepitaxy remain poorly understood. Here, we systematically investigate metal–organic chemical vapor deposition growth of MoS₂/WS₂ and WS₂/MoS₂ vertical heterostructures across varying interlayer thicknesses (monolayer to multilayer) and substrates (Si, SiO₂ and c-sapphire). We identify a substrate-field-modulated “remote–van der Waals (vdW) hybrid epitaxy” regime, in which vertical overgrowth is confined to a narrow thickness window (~ 1–3 layers), with nucleation density strongly influenced by substrate polarity and defect chemistry. High-resolution STEM reveals that, in the regions where vertical growth occurs, the in-plane crystallographic registry is primarily governed by vdW coupling to the 2D template, yielding a highly preferred single-orientation registry across the examined regions for both stacking orders. This dual-control mechanism decouples growth propensity from epitaxial alignment, providing a scalable framework for synthesizing high-quality 2D vertical heterostructures with precisely engineered interfaces.</p> Graphical abstract <p></p>