InAs/InP self-assembled quantum dots (SAQDs) are promising active layers for optical devices for fiber-optic communication. Furthermore, they may be used for the fabrication of uncooled mid and far infrared detectors. InAs/InP SAQDs were grown by low pressure-metalorganic chemical vapor deposition, where As/P exchange reaction and growth interruption step play an important role. The InAs quantum dot (QD) stacks were successfully grown on (001) InP substrate and their optical properties were characterized. Far-infrared absorption peaks were observed at 819 cm<sup>-1</sup> (12.20 μm) and 518 cm<sup>-1</sup> (19.35 μm) at room temperature by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. Raman analysis showed that the peak at 819 cm<sup>-1</sup> was attributed to a plasmon related peak in the n-type InP substrate. On the other hand, the absorption peak at 518 cm<sup>-1</sup> was regarded as a peak related with intersubband transition in the InAs QDs, suggesting that room temperature operating quantum dot infrared photodetectors (QDIPs) can be fabricated. In situ monitoring of the QD evolution and stacking sequences were also discussed.