In this study, the thermal shock reliability of sintered Cu joints on SiC power device application was investigated. Firstly, sintered Cu joints were used to bond chips and substrate consisting of various materials to evaluate their bondability. Secondly, SiC dummy chips were bonded to DBC substrate and thermal shock test from −40 °C to 250 °C were performed both in the ambient atmosphere and in vacuum. Finally, the SiC MOSFETs bonded by sintered Cu joints were evaluated by power cycle test from 25 °C to 200 °C and the thermal conductivity was evaluated by T3ster equipment. The results showed the sintered Cu exhibited extremely high reliability during the thermal shock aging test in ambient atmosphere although inferior reliability was observed in vacuum. This phenomenon was investigated and explained by field-emission scanning microscope, energy-dispersive X-ray spectroscopy, and X-ray diffractometer.