This study examines whether STEM(Science, Technology, Engineering, and Mathematics) professionals in South Korea have wage penalty using pooled data of the standardized occupational information and Wage Survey of Korea. Findings illustrate that the occupation of STEM professionals require the high-level cognitive, interpersonal, and physical skills to deal with data, people, and things in workplaces, as well as the longest year of education and experience. However, the hourly wage of STEM professionals is significantly lower than that of non-STEM professionals. Furthermore, by using the quantile regression of earning equation, we find that the returns to STEM professionals decrease more at the upper percentiles of the wage distribution, which means that wage penalty increases when the skill level is higher.