As deep earth oil exploration transits into deeper earth, it faces challenges in producing reliable microelectronics devices and sensors that will not degrade under a higher temperature and pressure environment. Numerous physical issues limit the manufacturing of this type of reliable microelectronics devices, especially those related to packaging materials and assembly of the microelectronics devices. One of the key requirements in reliability will be a continuous operating time of more than 500 h at 300°C. It is reported that the mechanical performance of a high temperature Au-Ge eutectic alloy is able to fulfill the minimum interconnection properties specified by the oil and gas exploration industry. However, the impact of thermal aging to Au-Ge eutectic alloy electrical property is not clear. The electrical resistivity of thermally aged Au-Ge eutectic alloys has been evaluated in this study. It is observed that the electrical resistivity decreases with thermal aging time until saturation. This effect is mainly contributed by the grain growth of Au, which results in a reduction in grain boundaries, thus causing a decrease in electrical resistivity. It has been determined that Au-Ge eutectic alloy is a suitable interconnection material in term of its electrical property to be used for high temperature electronics packaging.