We report results of a scanning tunneling microscopy investigation of the process of hydrogen adsorption on bismuth-deposited Si(111) surfaces. Two domains with the √3 × √3 periodicity are contained in the Si(111)(√3 × √3)-Bi surface, i.e., a low Bi-coverage √3 domain (named α-phase) and a high Bi-coverage √3 domain (β-phase). When atomic hydrogen adsorbs on the Si(111)(√3 × √3)-Bi surface, we found that (1) hydrogen atoms adsorb on the α-phase in preference to the β-phase, (2) Bi atoms are displaced from their original positions, and (3) bulk-like 1 × 1 surface structures appear in the restlayer. © 1998 Elsevier Science B.V.