A new procedure to obtain accurate SIMS depth profiles of Na in SiO₂ has been studied. SiO₂/Si samples implanted with Na were treated with HF solution to etch off a certain volume of the oxide. The surface was analysed with SIMS after being coated with Ag. The Na⁺ intensity at the Ag/SiO2 interface was plotted against the etched off depth and thus the depth profile of Na was obtained. This procedure is useful and easy to perform. It needs no special devices nor systems and has a possibility of wide application to various SiO₂ samples.