This paper discusses the design issues of highly efficient and monolithic wideband RF polar transmitters, especially the ones that use the EnvelopeTracking (ET) technique. Besides reviewing the stateof-the-art polar transmitters in the literature, three focus topics will be discussed: (1) the system-on-achip (SoC) design considerations of the monolithic polar transmitter using ET; and (2) the design of highly-efficient envelope amplifier capable of achieving the high efficiency, current, bandwidth, accuracy and noise specifications required for wideband signals; and (3) the design of highefficiency monolithic Si-based power amplifiers (PAs) suitable for ET-based RF polar transmitters.