An ultrahigh vacuum field-emission transmission electron microscope (UHV-FE-TEM) has been newly developed for the observation of semiconductor surfaces. It provides ultrahigh vacuum environment of 2.0 x 10(-8) Pa for surface studies, in addition to high contrast electron probe with large beam current for high-resolution transmission electron microscopy (HRTEM). Nanometric surface analysis using energy dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS) can be carried out simultaneously with HRTEM. Deposition of Mo onto both as-prepared and cleaned Si (111) TEM samples was performed at room temperature. HRTEM and EDS analysis suggest the formation of Mo nanocrystals. The size of the nanocrystals was about 2-3 nm on as-prepared sample, and 10-15 nm on cleaned sample. Electron beam irradiation resulted in the formation of Mo-related compound in as-prepared sample case, and sputtering or sublimation of Mo and Si in cleaned sample case.