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Infrared (IR) multispectral detection is attractingincreasing interest with the rising demand for high spectralsensitivity, room temperature operation, CMOS-compatible devices.Here, we present a two-terminal dual-band detector, which providesa bias-switchable spectral response in two distinct IR bands. Thedevice is obtained from a vertical GeSn/Ge/Si stack, forming adouble junction n-i-p-i-n structure, epitaxially grown on a Si wafer.The photoresponse can be switched by inverting the bias polaritybetween the near and the short-wave IR bands, with specificdetectivities of 1.9 × 1010 and 4.0 × 109 cm·(Hz)1/2/W, respectively.The possibility of detecting two spectral bands with the same pixelopens up interesting applications in the field of IR imaging andmaterial recognition, as shown in a solvent detection test. Thecontinuous voltage tuning, combined with the nonlinear photoresponse of the detector, enables a novel approach to spectral analysis,demonstrated by identifying the wavelength of a monochromatic beam.