According to this data chart [kff.org], about 30% of physicians are female.
As time go on, this will even out. While the ranks of older physicians are male-dominated, females make up just slightly under half the medical school class in the US. In parts of Europe, they already make up the majority:
women make up 54 percent of physicians below the age of 35 in Britain, 58 percent in France and almost 64 percent in Spain, according to the latest figures from the Organization for Economic Cooperation and Development