Abstract: A hydrogen indium-vacancy comples V_InH₄ in undoped and Fe-doped liquid encapsulated Czochralski (LEC) InP is measured by infrared absorption spectroscopy. This complex is found to be a common defect in as-grown LEC InP. The concentration of V_InH₄ in Fe-doped InP is higher than that of undoped InP. The concentration of V_InH₄ is high in wafers from the top of an ingot and low from the tail of an ingot. The influence of this complex on the electrical properties of n-type LEC undoped and compensation in Fe-doped InP is discussed. The results reveal the influence of V_InH₄ on the thermal stability of InP materials due to the fact that bond of hydrogen complex is weak and dissociates easily upon annealing.