Silicides have been used extensively in ULSI logic device fabrication as contact materials for the active areas as well as the poly- Si gates. NiSi is a promising candidate for submicron device application due to less volume expansion, low formation temperature, little silicon consumption, and large stable processing temperature window. In this report, the microstructure of nickel silicides fabricated with a thermal evaporator has been investigated. We observed systematic transformation of Ni silicides of $Ni_2$Si, NiSi, $NiSi_2$, as annealing temperature increases. All the silicides have been identified by a X-ray diffractometer (XRD). The cross-sectional microstructure of silicides was examined by a transmission electron microscope (TEM) equipped with a energy dispersive spectrometer(EDS). The surface roughness of silicides was measured by scanning probe microscope(SPM). Although we observed thin oxide layer existed at the $Ni/NiSi_{x}$ interface, we fabricated successfully $550AA$-thick planar Ni-monosilicide at the temperature range of$ 400~700^{circ}C$.