The effect of post-growth rapid thermal annealing on 35-layer In 0.50Ga 0.50As/GaAs quantum dot infrared photodetector (QDIP) with quaternary In 0.21Al 0.21Ga 0.58As capping has been investigated. Transmission electron microscopy showed some as-grown defects were removed by post growth annealing treatment. An increase in the compressive strain in the heterostructure due to annealing was identified from X-ray diffraction curve. A two-color photoresponse in the long-wave region (8.5 and 10.2 μm) was observed in both as-grown device and those annealed at 650 °C temperature. A three-fold enhancement in peak responsivity was observed in the QDIPs annealed at 650 °C (1.19 A/W) compared to that in the as-grown (0.34 A/W). Detectivity also increased by two fold from as-grown to 650 °C annealed device. The changes are attributed to the removal of as-grown defects and dislocations during epitaxial growth. These removals changed the confinement potential profile, which resulted in an improvement in the detectivity and responsivity of the annealed sample. © 2012 Elsevier Ltd. All rights reserved.