After a decade-long development effort, GaN-on-Si power devices have turn a new leaf with 600/650V transistors in mass production for several years, accumulating >4 billion device hours in the field at a low ppm failure rate. This along with recent success in 650V automotive-grade devices and 900V devices will help expand the GaN power semiconductor market at 35% compounded growth to exceed $1 billion by 2027 as predicted by IHS Markit. This tutorial offers a comprehensive look at how the high-voltage GaN devices complete a full cycle of technology validation: from device design, manufacturability and reliability to system economics, user satisfaction and ppm field failure rate. Topics to cover include: 1) GaN's true worth as a power semiconductor, 2) device structural choices, properties and performance, 3) competitiveness over Si and SiC counterparts, 4) application design wins including titanium-grade PSUs for computing and compact USB-C fast chargers for laptops/smart phones, 5) reliability and quality requirements for low ppm-level failure rates. The intended audiences are engineers at or above intermediate level in power electronics but with no requirement for GaN device knowledge.