I. Introduction
From a historical perspective, the development of semiconductor technologies has been driven by the ever-increasing need for improved electrical performance. Interestingly, however, it has been the thermal performance that often induced major changes to the direction of the technology development in recent years. Measured effect of ambient temperature on cutoff-frequency of high-speed SiGe HBTs, which shows the importance of thermal effects on semiconductor devices. The rapid replacement of the bipolar logic with the CMOS logic for high-speed digital applications in early 1990s was triggered by excessive heat generation from bipolar transistor-based integrated circuits. A decade later, the most advanced CMOS-based integrated circuits of today are confronting the same issue, the long-term direction of CMOS technology development being affected by the approaches on how to cope with such thermal problems. The thermal effects, or heat generation from self-heating and consequent junction temperature rise, adversely affect semiconductor device performance in terms of both functional operation and reliability.