Abstract Laser scanning microscope (LSM) based waveform acquisition is widely used in advanced CMOS IC design validation and debug application. Complex waveforms obtained from LSM probing on CMOS ICs are often difficult to fully comprehend without deep understanding of the complex physics involved even in planar CMOS. The introduction of 3-D Tri-Gate transistors since 2010 made this even more challenging. In this paper, we present both model based simulation and probing validations on the most advanced 3D Tri-Gate based CMOS ICs that give us a clear understanding of the nature of these complex waveforms.