Abstract Two-dimensional (2D) van der Waals (vdWs) heterostructures offer a versatile platform where engineered interlayer coupling enables optical processes beyond those of individual materials. Their atomically sharp interfaces support charge-transfer states, directional carrier transport, and broadband light-matter interactions, making them promising for advanced optoelectronics. However, the role of interlayer charge-transfer states in mid-infrared (MIR) photodetection remains insufficiently understood. Here, we demonstrate that a vertically stacked SnS 2 /InSe vdWs heterostructure enables an interlayer charge-transfer process that extends the photodetection range to 2500 nm, surpassing the intrinsic absorption limits of the constituent layers. The device achieves a high responsivity of 281 A W -1 and an external quantum efficiency of 62,360.6% at 532 nm, representing enhancements of up to 10 4 compared to individual SnS 2 and InSe devices. Density functional theory calculations reveal a reduced interlayer bandgap of 0.55 eV, which is consistent with the experimentally observed photoresponse measured up to 2500 nm. The device also exhibits polarization sensitivity, with a dichroic ratio of 1.35 at 1064 nm, and maintains stable operation under repeated 100 th cycling. These results highlight the potential of SnS₂/InSe vdWs heterostructures for broadband and MIR photodetection driven by interlayer charge-transfer states.