Herein, we demonstrated the fabrication of MoSe2/Si heterojunctions for high‐speed, broadband response photodetectors. High‐quality p‐n heterojunctions were formed by combing the p‐type Si substrate with n‐type MoSe2 film, thus bypassing the difficulty in controllable doping of MoSe2. More importantly, the MoSe2 film possessed a unique vertically standing layered structure, enabling the fast separation and transport of photogenerated carriers. Graphene (Gr) transparent electrode was adopted to further enhance the carrier collection and consequently reduce the recombination at junction interface. Significantly, the Gr/MoSe2/Si heterojunction photodetector exhibited a wide photoresponse range of 350–1310 nm and an extremely fast response speed of ≈270 ns, which represent the best values reported thus far for MoSe2 or MoS2 based photodetectors (Table 1 ).43, 44, 45, 51, 52, 53, 54 It is expected that the MoSe2/Si heterojunctions will have important applications for high‐performance optoelectronic devices.