A new process based on Boron diffusion step to improve the SiO2/SiC interface quality is presented in this work. Surprisingly, Boron, a p-type dopant and small size atom, generates similar apparent improvements as previous oxide treatments based on large size atoms, n-type or deep levels dopants. This process has been applied to a thermal oxide grown to fabricate large area (up to 25mm2) 4.5kV 4H-SiC VDMOS. Fabricated devices show a significant improvement in terms of channel effective mobility, on-resistance, and 3rd quadrant behavior in comparison with counterparts without Boron oxide treatment.