Leaded frits in Ag pastes have generally been used to fabricate Ag electrodes. The bismate glass system has been reported to be an appropriate frit for use in Ag pastes for eco-friendly materials. The characteristics of bismate frits under fast firing were first studied to elucidate the phenomena occurring in the molten glass. To determine the reactions among Ag, frits, and an Si wafer coated with SiNx, the interfacial structures between Ag electrodes and the Si wafer were investigated using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy coupled with EDX, and X-ray photoelectron spectroscopy. The precipitates formed in the molten frits were found to be Bi nanoparticles. The interfacial structures between the Ag electrodes and the Si wafer consisted of Ag electrodes, glass layers, and recrystallites formed in the n+ emitter. The recrystallite elements existed as Ag–Si and Ag–Bi–Si, which are segregated, as well as Ag. These results suggest that the contact formation between the Ag electrodes and the Si wafer was caused by the characteristics of bismate frits in Ag pastes under fast firing.