The aim of this study is to characterize a die attach method suitable for harsh environment as well as high reliability applications. Au-Au thermosonic bonding was selected. Due to high melting temperature of gold, this technique suited well for high temperature applications. In addition, thermosonic bonding introduces ultrasonic energy to soften the material joint and enhance the bonding at the metallic interface. This allows reducing the bond temperature and force. Initial characterization focuses on the effects of bonding parameters - ultrasonic energy, bond force and bond temperature - to relative bond strength. Bonded components were subjected to die shear test to measure bond strength. Cross section and SEM were used to inspect the bond interface and Aubump deformation. Thermal shock cycling (TSC) test performed from -20 to 200°C was carried out to examine bond reliability. Experiment results were compared to thermocompression bonding to evaluate the improvement of thermosonic bonding. Initial experiments showed that we obtained successful bonding at temperatures as low as 50°C. Maximum shear strength measured was around 400 g/bump. TSC significantly reduced bond strength, but high shear force remained after TSC ranging from 82 to 140 g/bump. Therefore, thermosonic bonding offers high reliability, low temperature and low force process.