The book gives a detailed presentation of high-frequency bipolar transistors in silicon or silicon-germanium technology with particular emphasis placed on today's advanced compact models and their physical foundations. The first part introduces the fundamentals of bipolar transistors on a graduate-student level. The second part considers the physics and modeling of bipolar transistors in detail. The final part describes basic circuit configurations, aspects of process integration and applications. This modern book-length treatment will interest those working in the field, including circuit designers, industrial process developers, and PhD students.