The 18-year-old South African champ has no womb or ovaries and her testosterone levels are more than three times higher than those of a normal female, according to reports.
Semenya has been dogged by questions about her gender since easily winning the 800-meter gold medal last month in Berlin at the world championships.
Semenya could be stripped of the gold medal she won and her competitive future is in limbo, according to Australia's Daily Telegraph.
Her dominating run came on the same day track and field's ruling body said she was undergoing a gender test because of concerns she did not meet requirements to compete as a woman.
In the race, Semenya took the lead at the halfway mark and opened a commanding lead in the last 400 meters to win by a massive 2.45 seconds in a world-leading 1 minute, 55.45 seconds. Defending champion Janeth Jepkosgei was second and Jennifer Meadows of Britain was third in 1:57.93.
A gender test was ordered, officials say, not because Semenya was suspected of cheating by having had a sex change operation, reports CBS News correspondent Mark Phillips, but to determine whether she has what's being called "a medical condition."
"I don't know who said it... I don't give a damn about it," Semenya told a television crew after the race in August.
Her dramatic improvement in times, muscular build and deep voice sparked speculation about her gender. Ideally, any dispute surrounding an athlete is dealt with before a major competition. But Semenya's stunning rise from unknown teenage runner to the favorite in the 800 happened almost overnight.