There have been various studies showing that InP-InGaAs quantum-well infrared photodetectors (QWIPs) are potential alternatives to AlGaAs-GaAs QWIPs in the long wavelength infrared (LWIR) band, especially for applications requiring high responsivity. Being on InP substrate, this material system also offers lattice matched mid-wavelength infrared (MWIR)/LWIR dual band QWIP stack when it is used with the AlInAs-InGaAs system. It is desirable to extend the cut-off wavelength of Inp based LWIR QWIPs to similar to 9 mu m, which can be accomplished by replacing the QW material with InGaAsP. In this paper, we report the first InP-InGaAsP QWIP focal plane array (FPA). The 640 x 512 FPA displayed remarkably low noise equivalent temperature difference (NETD) with very short integration times'(46 mK at 66 K with T-int = 440 mu s and f/1.5 optics). The results show that these QWIPs can be operated with high responsivity (> 1 A/W) while offering bias adjustable gain in a wide range where the detectivity is almost constant at a reasonably high level.