SiGe HBTs and their circuit technologies are suitable for future wireless communications. To achieve low 1/f-noise characteristics in RF applications, a SiGe HBT with a raised-emitter structure, fabricated by epitaxial growth of phosphorous-doped Si layers, was developed. Aimed at ultra-low power consumption in a wide range of microwave applications, a SiGe HBT fabricated by well-controlled SiGe/Si continuous epitaxial growth was developed. To improve the design process for Si-based RF-ICs, equivalent circuits for transmission lines under the slow-wave effect and for inductors under the peripheral ground effect were also demonstrated. Moreover, MMICs operating in the quasi-millimeter-wave region, namely, two 24-GHz LNAs, a 27-GHz VCO, and a 24-GHz mixer were developed. In regards to these MMICs, new circuit technologies, namely, inductive biasing, merged transformer matching, and pseudo-stacked configuration, were developed.