From da wiki:

Semenya has the intersex condition 5α-Reductase 2 deficiency, which only affects genetic males. Individuals with this condition have normal male internal structures that are not fully masculinized during the embryo's development, resulting in external genitalia that appear ambiguous or female at birth. Although Semenya was assigned female at birth, she has XY chromosomes, undescended testes, and naturally high testosterone levels in the typical male range. However, Semenya has rejected the label of "intersex," calling herself "a different kind of woman."