UBS, which offers wealth-management services, tallied 1,347 billionaires from around the world in the study but declined to name any of them.
Men still accounted for the overwhelming majority of billionaires, but women made up 11 percent last year, up from 9 percent two decades earlier.
Asia has seen the strongest growth rates for female billionaires over the last decade, to 25 from three.Just over half of the female Asian billionaires made their own money, UBS said, with many of the women hailing from China and Hong Kong and much of the wealth coming from real-estate investments.
UBS said only 7 percent of European women billionaires and 19 percent of the Americans were self-made.