Recently, a plethora of applications has emerged that can take advantage of the mm – wave frequency band characteristics, i.e. high bandwidth, small form factor etc. Applications at mm-wave frequencies include smart sensors, single chip phased-arrays etc. For many years, III-V technologies were the main driving technologies for circuits operating at high frequencies. However, recent advances in silicon processes have enabled the use of BiCMOS and CMOS technologies as enablers for circuits and systems operating at mm-wave and sub-mm wave frequencies, i.e. frequencies above 100GHz. Hence, high frequency and baseband electronics can be integrated in a single chip, thus reducing cost dramatically. The ultimate goal is to have silicon circuits operation at Terahertz frequencies. The need for power generation at high frequencies is fundamental for the successful implementation of any application. There is a variety of circuits providing power at frequencies below 100GHz, namely oscillators and power amplifiers. Furthermore, lasers and other optoelectronic devices are capable of providing power above 10THz. Hence, there is a gap in power generation between 100GHz and THz that has to be filled in order for the applications to be accommodated. This thesis constitutes an effort towards the direction of understanding the challenges and limitation of power generation at frequencies above 100 GHz. Specifically active and passive device limitations are addressed and guidelines are given in order for the best performance possible to be achieved. The acquired knowledge is applied in the design of a medium output power PA at 135 GHz. Specifically, the PA achieves an -1dB compression point output power of 5dBm and a saturated output power of 8 dBm along with a power gain of 17 dB.