To date, scale-up fabrication of transition metal dichalcogenide (TMD-) based 2D/2D or 2D/3D heterostructures with specific functionalities is still a great challenge. This study, for the first time, reports on the controllable synthesis of large-area and continuous 2D/3D semiconductor/metal heterostructures consisting of monolayer MoS2 and bulk MoO2 with unique electrical and optical properties via one-step, vapor-transport-assisted rapid thermal processing. The temperature-dependent electrical transport measurements reveal that the 2D/3D MoS2–MoO2 heterostructure grown on SiO2/Si substrates exhibits metallic phase, while this heterostructure becomes a low-resistance semiconductor when it is grown on fused silica, which is attributed to the different degrees of sulfurization on different substrates, as being confirmed by surface potential analyses. Photoluminescence measurements taken on the MoS2–MoO2 heterostructures reveal the simultaneous presence of both negative trions and neutral excitons, while only neutral excitons are observed in the monolayer MoS2. The trion-binding energy is determined to be ≈27 meV, and the trion signal persists up to 330 K, indicating significant stability at room temperature. This work not only provides a new platform for understanding the intriguing physics in TMD-based heterostructures but also enables the design of more complicated devices with potential applications in nanoelectronics and nanophotonics.Read less <