Tests indicate her testosterone levels are triple that of an average female.  Apparently this is true and that they had the results before the world championships.  No kidding!!

http://www.mirror.co.uk/sport/more-sport/2009/08/24/gender-row-athlete-caster-semenya-has-high-levels-of-male-hormone-115875-21621631/

 Normal testosterone for a peak healthy female is 50-100 ng/dl and for men it can range from 200-1200.  The maximum testosterone level occurs in the 20s for men

http://www.thebody.com/content/art32237.html

This next section is speculation!!

Do not look at this next if you don't want to look at the possibility of hermaphrodism

The big question is if he is a hermaphrodite.  If that is the case, it makes the most sense.  Research of a patient showed half the normal level of testosterone. 

http://smj.sma.org.sg/3701/3701cr4.pdf