This study investigates gender differences in labor market outcomes among highly educated individuals in Japan, emphasizing heterogeneity by fields of study, with a focus on STEM. Using data from the Japanese Panel Study of Employment Dynamics (JPSED), we find that women with STEM degrees begin their careers with earnings comparable to men with at least a bachelor’s degree in any field; yet the gap widens to 24.4 percent six to ten years after graduation. Penalties are especially large for mothers and remain sizable for childless women. Field differences are stark: six to ten years out, women with STEM bachelor’s degrees, Social Sciences, or Humanities degrees earn less than men with high-school or junior-college education. In contrast, women with STEM advanced degrees or Medicine/Pharmacy degrees earn more than men with a high-school or junior-college education, and women with Medicine/Pharmacy degrees maintain wage parity with men holding at least a bachelor’s degree in any field. These findings indicate that family responsibilities matter, but structural barriers against women also contribute to persistent gender gaps, with holders of advanced degrees in STEM, Medicine, or Pharmacy as notable exceptions.