Using microdata between 1998 and 2020, this study provides potential explanations for the gender wage gap in South Korea, which continues to be the largest among Organisation for Economic Co-operation and Development (OECD) countries. Although improvement in females’ relative measured labor market characteristics plays an important role in the reduction of the gender wage gap, these characteristics cannot explain a large part of the gap, and wage convergence between full-time male and female workers has slowed over the period. Indeed, the unexplained gender wage gap has become larger than the explained gender wage gap. This is confirmed when a decomposition of the gender wage gap is performed across the wage distribution. This study provides evidence of the existence of a glass ceiling. In addition, this study shows that, in South Korea, where conservative gender-related norms still persist, the effects of marriage and childbirth can help to account for a dramatic increase in the gender wage gap for female workers in their 30s and 40s.