p-InP (100) was electrochemically sulfur passivated in (NH4)2Sx solution, and the resulting surfaces analyzed by XPS, AES, and SEM.It was found that one monolayer of sulfur adsorbed on the InP surface at potentials below 0.3 V (vs. SCE); while at potentials above 0.3 V,a 3-dimensional In2S3 layer was formed. Conditions for preparation of a continuous, 150 nm thick In2S3 passivating layer have beendetermined. ; peer reviewed: yes ; NRC Pub: yes