p-InP (100) was electrochemically sulfur passivated in (NH4)(2)S-x 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 been determined.