InP homoepitaxial layers and heteroepilayers of LnP grown on (001) and (111)B surfaces of GaAs substrates by metalorganic chemical vapor deposition, have been investigated using time-resolved photoluminescence spectroscopy. In this study, we have focused on the intrinsic transitions. The measured decay-time for the heteroepitaxial layers of InP exhibited the same temperature dependence as the thermal quenching. The decrease of the decay-time as the temperature increase is attributed to the non-radiative processes, which are thermally activated. It is shown, by comparison with InP homoepitaxial layers, that the PL decay-time for InP on both (111)B and (001) surfaces of GaAs substrates is decreased. The reduction of the measured decay-time is considered to be due to the additional non-radiative processes arising from the threading dislocations. Compared with the InP on GaAs(001), the heteroepilayers on GaAs(lll)B substrates exhibited a significant increase in the decay time as a result of the reduction in the threading dislocations density.