A hydrogen indium vacancy complex VlnH4 in undoped and Fe-doped liquid encapsulated Czochralski (LEC) InP is measured by infrared absorption spectroscopy in wafers sliced from the seed-end, middle and tail of an ingot. The concentration of VlnH4 is found much lower in wafers sliced from the ingot rail. The concentration of VlnH4 in Fe-doped InP is higher than that of the undoped InP. The concentration change of VlnH4 in an InP ingot is qualitatively in agreement with the mass action law expectation based on defect reactions. The influence of this complex on the electrical properties of n-type LEC undoped and Fe-doped InP is discussed. The high concentration of VlnH4 in the seed-end of an InP ingot correlates with two facts. The first is the high threshold concentrations of Fe and Zn required to get semi-insulating and p-type material, respectively. The second is that there is a large thermally induced reduction of carrier concentration in seed-end InP wafers than that of wafers From the ingot tail. The results reveal the influence of VlnH4 on the thermal stability of InP material due to the fact that the bond of hydrogen complex is weak and dissociates easily upon annealing. This dissociation has a relationship with the defects formed in high-temperature annealed InP, which are involved in the electrical compensation.