Women don't negotiate comp as often as men do. They leave money on the table. It's somewhat of an open secret among execs who have managed large teams inside these companies. Absent a cultural shift among women to ask for more (which they should, because they'd get it - and rightfully so as they are doing the same work), there aren't a lot of great solutions to this. Do you narrowly fix comp like law firms do for associates? Do you assign each employee a headhunter to negotiate on their behalf? Each potential solution creates other problems. It's fair to point out that this is a problem outside of tech also, but the rapid growth in salaries in tech, and especially in the Bay Area, have made the disparity more extreme and noticeable.