Molybdenum disulfide (MoS ), a typical 2D metal dichalcogenide (2DMD), has exhibited tremendous potential in optoelectronic device applications, especially in photodetection. However, due to the weak light absorption of planar mono-/multilayers, limited cutoff wavelength edge, and lack of high-quality junctions, most reported MoS -based photodetectors show undesirable performance. Here, a structurized 3D heterojunction of RGO-MoS /pyramid Si is demonstrated via a simple solution-processing method. Owing to the improved light absorption by the pyramid structure, the narrowed bandgap of the MoS by the imperfect crystallinity, and the enhanced charge separation/transportation by the inserted reduced graphene oxide (RGO), the assembled photodetector exhibits excellent performance in terms of a large responsivity of 21.8 A W , extremely high detectivity up to 3.8 × 10 Jones (Jones = cm Hz W ) and ultrabroad spectrum response ranging from 350 nm (ultraviolet) to 4.3 µm (midwave infrared). These device parameters represent the best results for MoS -based self-driven photodetectors, and the detectivity value sets a new record for the 2DMD-based photodetectors reported thus far. Prospectively, the design of novel 3D heterojunction can be extended to other 2DMDs, opening up the opportunities for a host of high-performance optoelectronic devices.