© 2017 IEEE. This report studies the influence of printed circuit board (PCB) design on voltage overshoot and ringing oscillation in switching operation of gallium nitride gate injection transistor (GaN-GIT) for high-frequency DC-DC converter. The parasitic inductances in the main power loop have been identified based on moment of method (MoM) analysis and frequency characteristics of impedance measured with 2-port shunt-thru method. The measured switching characteristics of GaN-GIT in a 5 MHz DC-DC boost converter shows that a small-ESL ceramic capacitor connected across the DC-link can reduce the effective power loop inductances and can improve both voltage overshoot and the damping of ringing oscillation.