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• Microstructural and mechanical stabilities of 30Ni-70Sn TLPS joints are analyzed. • The microstructures of Ni 3 Sn 4 intermetallics around Ni particles are dense and stable during aging. • The initial strengths maintained even after aging for 1000 h at 150 and 200 °C. • Ni-Sn paste is effective as a die attach material for power electronic devices. In this study, the feasibility and high-temperature stability of Ni-Sn bonded joints fabricated by transient liquid phase sintering (TLPS) were investigated for high-temperature power electronics applications. A 30Ni-70Sn (wt%) TLPS paste was fabricated with micro-sized pure Ni and Sn powders, and chip bonding was performed on a direct bonded copper (DBC) substrate. During TLPS bonding, Sn particles melted and reacted with Ni particles, which resulting in the formation of stable Ni-Sn TLPS intermetallic joints. During aging treatments at 150 and 200 °C, the formed Ni 3 Sn 4 phases were transformed into the Ni 3 Sn 2. With increasing aging treatments, the reactions between Ni 3 Sn 4 intermetallics and remaining Ni particles increased, which resulted in the formation of the Ni-rich Ni-Sn intermetallics. Even after 1000 h at an aging temperature of 200 °C, there is no significant difference in the stable and dense microstructure of Ni-Sn TLPS joints. In addition, their mechanical strengths did not vary significantly even after long-term treatment for 1000 h at 150 and 200 °C. This means that the Ni-Sn TLPS joints have a good long-term microstructural stability and mechanical reliability at high temperatures up to 200 °C. Therefore, we conclude that the Ni-Sn paste is a promising candidate as a die-attach material for high-temperature electronic assemblies. [ABSTRACT FROM AUTHOR]