We extend the conventional framework for measuring segregation to consider stratification of occupations by gender, i.e. when women or men are predominantly segregated into low-paying jobs. For this, we propose to use concentration curves and indices. Our empirical analysis using this approach shows that the decline over time in occupational gender segregation in the US has been accompanied by a deeper, longer reduction in gender stratification. We further investigate the role of workers' characteristics, showing that gender differences cannot explain the levels of segregation/stratification in any year. However, changes over time for each gender do help to explain their trends.