I. Introduction
State-Of-The-Art heterojunction bipolar transistors (HBTs) and power amplifiers (PAs) are inevitably constrained in power performance by thermal-dissipation issues [1]. Heat management and size shrinkage of HBT-based PAs are significant to the development of miniature handset wireless systems. Several researches have proposed specific configurations to enhance the thermal stability of GaAs-based HBTs [2]–[5]. However, current conceived structures, such as through-wafer vias, ballasting resistors, and thermal shunts, employed in advanced power HBTs are not cost-effective for high-efficiency PA applications. Regarding next-generation cellular phones, the smallest PA with high-thermal-dissipation capability is a must. Furthermore, it is crucial to alleviate the temperature-interference effect between fingers of the multifinger HBT, particularly during high-power operation for the advancement of power-added efficiency (PAE) and reliability.