The effect of phosphorus (P) on the electrical properties of the 4H-SiC/SiO2 interface was investigated. Phosphorus was introduced by surface-near ion implantation with varying ion energy and dose prior to thermal oxidation. Secondary ion mass spectrometry revealed that only part of the implanted P followed the oxidation front to the interface. A negative flatband shift due to residual P in the oxide was found from C-V measurements. Conductance method measurements revealed a significant reduction of density of interface traps Dit with energy EC-Eit > 0.3 V for P+-implanted samples with [P]interface = 1.5 · 1018 cm-3 in the SiC layer at the interface. .