It is shown that both acceptors and donors can be passivated by hydrogen in InGaP and InGaAlP and that high-resistivity (about 103 Ω cm) layers of p-InGaAlP and of p-InGaP can be prepared by hydrogen plasma treatment at 250°C. Proton implantation with energy 100 keV is shown to create high-resistivity layers (104-105 Ω cm) both in n and in type InGaP and InGaAlP. © 1995.