This article describes an innovative technique to perform real-time oscilloscope-based nonlinear VNA trap measurements of IV characteristics of GaN HEMT devices. The technique measures the evolution of an RF load line prior to steady-state operation of the device instead of tediously measuring one point on the IV curve at a time with alternative methods. Isothermal, pulsed, large-signal measurements can be performed and tracked across the entire sequence of pulses. The method is also useful for multiharmonic modulated signals measurement for devices operating in class B and for real-time active load pull (RTALP) measurements.