2D van der Waals heterostructures with different types of band alignment have recently attracted great attention due to their unique optical and electrical properties. Most 2D heterostructures are formed by transfer-stacking two monolayers together, but the interfacial quality and controllable orientation of such artifcial structures are inferior to those epitaxial grown heterostructures. Herein, for the frst time, a direct vapor phase growth of high-quality vertically stacked heterostructure of SnS2/MoS2 monolayers is reported. An extremely Type II band alignment exists in this 2D heterostructure, with band offset larger than any other reported. Consistent with the large band offset, distinctive optical properties including strong photoluminescence quenching in the heterostructure area are observed in the heterostructure. The SnS2/MoS2 heterostructures also exhibit well-aligned lattice orientation between the two layers, forming a periodic Moiré superlattice pattern with high lattice mismatch. Electrical transport and photoresponsive studies demonstrate that the SnS2/MoS2 heterostructures exhibit an obvious photovoltaic effect and possess high on/off ratio (>106), high mobility (27.6 cm2 V-1 s-1) and high photoresponsivity (1.36 A W-1). Effcient synthesis of such vertical heterostructure may open up new realms in 2D functional electronics and optoelectronics.