Power semiconductor devices for electric power conversion must be highly efficient, compact, and with large capacity. Therefore, highly thermo stability and long fatigue lifetime are necessary for the joint materials of these devices. In this paper, we discuss the joint reliability obtained by applying the supersaturated Sn-13wt. % Sb binary alloy. Through this process, the joint materials achieve a thermo stable up to 175 °C or more. Thus, they can be used in wide-bandgap semiconductors to join the ceramic substrate with the heat sink. Finally, we examine the new material properties (tensile and low cycling fatigue). The thermal cycling lifetime of supersaturated Sn-Sb joints is significantly affected by the material's microstructure; when its crystal grains are large, the material has a longer lifetime. Consequently, in SbSn compounds, which crystallize in the β-Sn matrix, solder crack propagation can be prevented when the compound is large enough; there is a mechanism that suppresses the propagation speed of the crack. In addition, the supersaturated Sn-13wt. %Sb binary alloy is also resistant up to 150 °C, above the higher temperature at which the joints are exposed to. Therefore, this application can ensure high reliability for the high temperature operating devices, which operate at 175 °C temperature or higher.