Abstract: In a system consisted of semiconductor silicon wafer (Si), diffusion resistant layer (Cr-Ni alloy) and metal contact material (Cu), diffusion couples were formed at Si/(Cr-Ni) and (Cr-Ni)/Cu, respectively. The phases formed due to interracial reactions in both the diffusion couples were investigated experimentally and the apparent phase contact sequences were obtained at 950℃. Based on phase equilibrium calculations of the Cr-Cu-Ni and the Cr-Ni-Si ternary systems, the phase formation driving forces for interfacial reactions of the diffusion couples were analyzed theoretically. The step-by-step phase formation sequences were obtained to simulate microstructure evolutions in the diffusion couples. The thermodynamic predictions are in accord with the experimental observations.