Using the inherent properties of a heterostructure, ultrafast photodetectors with high sensitivity can be progressively developed that have the potential to carve a niche among the optoelectronic devices. In this Letter, a heterojunction photodetector based on SnSe2/Bi2Se3 is constructed, and a visible-infrared photoresponse with good sensitivity at room temperature is obtained. The SnSe2/Bi2Se3 photodetector demonstrates a high Iph/Id ratio of 1.2 × 104 at 0 V. Moreover, the high responsivity of 2.3 A/W, detectivity of 1.6 × 1011 Jones, and fast response time of 40 µs are simultaneously achieved. The presented results offer an alternative route for ultrafast photodetectors with high sensitivity.