More compact power converters can be realized with the recently introduced gallium nitride (GaN) power devices. However, power board layout becomes more critical. In order to reduce switching losses, voltage overshoot and to achieve fast and safe drive, the stray inductances should be minimized. In this paper, a 5-phase DC-DC interleaved buck converter with an InterCell Transformer (ICT) integrated in a multilayer PCB using GaN EPC 100V devices is described. It appears that the routing of power decoupling capacitors is the result of a tradeoff between stray inductance and cooling with a single heatsink for the 5 phases. The power board (110mm×62mm, 51g) reaches 97% efficiency with a 48V to 24V conversion at 1.8kW and an effective output current frequency of 1.5MHz.