Positron annihilation spectroscopy on Zn‐doped InP has revealed the presence of a defect with a positron lifetime of ∼330 ps in samples in which the carrier concentration has saturated. This lifetime is attributed to a complex involving vacancies and Zn atoms. A model is proposed in which this complex has a (−/0) level near the bottom of the band gap, and undergoes a large inward lattice relaxation upon the transition to the neutral charge state, causing a reduction in the positron lifetime to ∼281 ps. This model explains the positron annihilation results on annealed samples and at low temperatures, and is supported by Hall effect measurements. The concentration of these complexes is less than 1017cm−3. Therefore, these complexes cannot solely account for the observed discrepancy between the carrier concentration and the Zn concentration in very heavily Zn‐doped InP. ©1996 American Institute of Physics.