Modern microwave communication systems continue to push on-wafer VNA measurements into the mmWave bands. Successful system design depends on optimum device characterization, generating well-defined device models, resulting in dependable circuit simulation. It has been demonstrated that characterizing devices well beyond 125 GHz dramatically improves device model accuracy, even for applications operating 60 GHz and below. As a result, the current incentive for on-wafer VNA measurements is to provide single-sweep coverage over an extremely wide frequency range to maximize the potential for first-turn design success. This WebTalk will discuss important aspects when performing ultra-wideband 220 GHz VNA measurements and will describe basic VNA architecture, choices in broadband VNA calibrations, and how to optimize VNA on-wafer measurement performance.