Domestic sales of the DSi reached 3,062,920 units as of August 2, according to new Enterbrain figures.
The updated console launched in Japan on November 1 2008, meaning the milestone has been reached in the space of just nine months, reports Famitsu.
Nintendo's latest quarterly financial results, released last week, showed that worldwide DSi sales for the three months ending June 30 had totalled 3.65 million. Worldwide, the system, which launched outside of Japan in April 2009, has sold 6.68 million units to date, confirmed the company.