Deep electron traps in n-InP introduced during plasma exposure have been studied by means of isothermal capacitance transient spectroscopy (ICTS). Three electron traps, (Ec
–0.21 eV), (Ec
–0.34 eV) and (Ec
–0.54 eV), which are designated E2, E3 and E4, respectively, are detected in n-InP treated with H2 plasma and by subsequent annealing. The E2 trap is induced by plasma exposure and the E3 trap is produced by thermal annealing. The E4 trap is generated by both plasma exposure and thermal annealing. These three traps are passivated with hydrogen atoms. The E2 trap density near the surface of hydrogen-plasma-treated samples is strongly enhanced by applying electric field because of dissociation of hydrogen from E2 trap. The E2 trap is annealed out with the activation energy of 1.5 eV and the attempt-to-escape frequency of 3.2 × 1014 s−1. Phosphine plasma treatment is effective in suppressing generation of these electron traps.