Abstract: This presentation discusses high power monolithic microwave integrated circuit (MMIC) power amplifier (PA) design in Gallium Arsenide (GaAs) and Gallium Nitride (GaN).  At a high level, GaN versus GaAs semiconductor technology from the perspective of power amplifier design metrics is analyzed to help determine the relative advantages and disadvantages of each technology.  This is followed with an introduction of the most prevalent MMIC design topologies for the bulk of microwave applications which include reactively matched, non-uniform distributed, balanced, push-pull, Doherty and serially combined.  Following introduction of the main topologies, the presentation focuses on the potential pitfalls the MMIC designer can encounter with detailed discussion on how to avoid them with the goal of first past design success.  The presentation relies on experience from the author’s career with over 20 years of experience in the defense and commercial industries as well as academia.  MMIC designers will appreciate the candid explanation of the design topologies and pitfalls while non-designers will come away with a good working knowledge of what can be achieved and what to watch out for.