Microstructure and atomic composition below Ni contact on n-type 4H- SiC were investigated and the results were compared with the electrical properties. When the Ni contact was annealed at 1000 degreesC, ohmic contact, corresponding to the SBH of 0.38 eV, was formed. Two kinds of Ni silicides, Ni31Si12 and Ni2Si, were observed at 600 degreesC and after annealing at 950 degreesC, the graphite and NiSi were newly produced. The formation of NiSi was also observed by XPS spectra near the interface, indicating that the composition of Si in nickel silicide forming at the interface of SIC increased with the elevation of annealing temperature. An abundance of C atoms were outdiffused to the surface of contact layer leaving C vacancies. C vacancies act as donors for electron, which increase the net concentration of electrons, resulting in the reduction of effective SBH for transport of the electrons, via, the formation of ohmic contact on n-type SiC.