Planar InP/In0.53Ga0.47As photodiodes with boro‐phospho‐silicate glass (BPSG) layers as a Zn‐diffusion mask and as an InP surfacep‐njunction passivant exhibit stable, reverse‐bias leakage‐current characteristics at 220 °C for more than 104h. Based on these results, estimates of the time required for the leakage current at 70 °C to saturate at 10 nA is, in the worst case considered, about 33 years. As a passivant and diffusion mask, BPSG compares favorably with silicon nitride.