A novel long-wavelength InP-based resonant cavity enhanced (RCE) photodetector is introduced. High-reflectivity InP/air gap distributed Bragg reflectors (DBRs) have been fabricated by the selective wet etching of InGaAs sacrificial layers with FeCl3∶H2O solution. And the technique has been successfully applied to the fabrication of long-wavelength InP-based RCE photodetector. Thus the problem, the unachievable epitaxy of high-reflectivity InP/InGaAsP DBR, is resolved. The mesa area of this type RCE photodetector is 50 μm×50 μm, the bottom mirror is 1.5 pairs InP/air gap DBR, the interface reflection of the air and InGaAsP layer serves as the top mirror. The measurement results show that the quantum efficiency of 59% at 1.510 μm wavelength, the dark current of 2 nA at 3 V reverse bias, and the 3 dB bandwidth of 8 GHz have been achieved.