This invited SPIE paper by Handel, Hall, and Morkoç examines quantum 1/f noise in GaN FETs, MODFETs, and their oscillators' phase noise. The research provides comprehensive analysis of low-frequency noise in gallium nitride field-effect transistors and modulation-doped FETs, and demonstrates how this baseband noise upconverts to phase noise sidebands in oscillator applications, offering theoretical predictions and design strategies for minimizing phase noise in GaN-based RF sources for radar, satellite communications, and high-power microwave systems.