A monolithic quantum well infrared photodetector (QWIP) structure has been presented that is suitable for dual bands in the two atmospheric transmission windows of 3 – 5.3 μm and 7.5 – 14μm, respectively. The proposed structure employs dual stacked, strain InGaAs/AlGaAs and latticematched GaAs/AlGaAs quantum well infrared photodetector for mid wavelength and long wavelength detection. The response peak of the strain InGaAs/AlGaAs quantum well is at 4.9 μm and the lattice-matched GaAs/AlGaAs is at 10.5μm; their peak sensitivities are in the spectral regions of 3 – 5.3mu;m and 7.5 – 14μm. The peak responsivity when the dual-band QWIP is biased at 5 Volts is ∼0.065A/W at 4.9μm and ∼0.006A/W at 10.5μm; at this voltage the dual-band QWIP is more sensitive at the shorter wavelengths due to its larger impedance thus exhibiting wavelength tunability characteristics with bias. Additionally, single colored 4.9 and 10.5μm QWIPs were fabricated from the dual-band QWIP structure to study the bias-dependent behavior and also to understand the effects of growing the strain layer InGaAs/AlGaAs QWIP on top of the lattice-matched GaAs/AlGaAs QWIP. In summary, two stack dual-band QWIPs using GaAs/AlGaAs and strained InGaAs/AlGaAs multiquantum wells have been demonstrated with peak spectral sensitivities in the spectral region of 3 – 5.3μm and 7.5 – 14μm. Also, the voltage tunable dual-band detection have been realized for this kind of QWIP structure.