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Recent trends in the semiconductor industry are driving a continuous increase in power dissipation, but require a lighter, more compact and thinner packaging technology. One of the concern areas is the increasing temperature of the C4 die bump. As the power continues to increase, the electrical current through the C4 die bump increases accordingly, resulting in increased bump temperature due to Joule self-heating and trace heating. The bump current density and temperature is now approaching levels where electromigration is a significant reliability concern. In order to fully understand and avoid this failure phenomenon, we need to know the C4 die bump temperature. However, the material property of the bump is also a major factor contributed to the bump temperature which must be evaluated. This paper discusses the methodology of measuring the C4 die bump temperature as well as results of our measurements. The experimental study includes variation of the bump current, the die power dissipation, different enabling thermal solutions and different bump materials. The experimental results show the effect of the Joule self-heating of the bump and the impact of the bump materials.