Bonding dynamics during ultrasonic bonding of Cu free air ball (FAB) is investigated by measuring dynamic strain with piezoresistive strain sensor. Change in dynamic strain with elevating substrate temperature up to 200°C was investigated. It was clearly observed that elevating substrate temperature significantly enhanced deformation of the Cu FAB while the application of pressing load and ultrasonic vibration. Visualization of the average strain clearly indicated that concentration of strain in the device layer at the positon over which the end of capillary was present was reduced. Therefore, elevating substrate temperature may reduce generation of damage in the device layer. It was also found that elevating substrate temperature reduced the residual strain in the device layer.