[en] Highlights: • Electron and positron energy levels in InP at various pressures. • Hydrostatic pressure effect on positron affinity and bulk lifetime in InP. • Positronium work function in InP under compression. • The information gathered from the present investigation is very useful in slow-positron-beam experiments. - Abstract: The electron and positron chemical potentials, positron affinity and bulk lifetime as well as the positronium work function in InP are investigated. The emphasis of this work is on the hydrostatic pressure effect on these features. The calculations are performed with a pseudopotential approach and the independent particle model. All parameters of interest are found to vary monotonically with pressure. Our findings showed that under compression the positron annihilates differently in InP semiconductor compound. At zero pressure, the positron bulk lifetime is calculated to be 243.47 ps. However, upon compression it decreases almost linearly suggesting the decrease of the crystal ionicity under applied pressure. The positronium work function is found to increase with raising pressure which indicates that under compression less positronium atoms will be formed in InP sample surface and ejected into the vacuum. The parameters investigated in the present work are important in slow-positron-beam experiments.