we grew compound semiconductor nanocrystals on passivated Si surfaces, which were characterized by photoelectron spectroscopy and RHEED (reflection high energy electron diffraction). The Ga-deposited Si(111) surface with a 1x1 RHEED pattern was significantly converted into GaSb nanocrystals by Sb beam irradiation at 500 degrees C. In order to grow better quality GaSb nanocrystals, Se-terminated Si surfaces were employed, and about 20 nm uniform GaSb nanocrystals were grown, whose crystallinity of good quality was verified by cross-sectional TEM. For InAs nanocrystals, hydrogen-terminated Si surfaces are suitable for growth at as low substrate temperature as 300 degrees C.