To investigate the extent to which Korean students benefit from English-medium instruction (EMI) in linguistics courses, we collected online survey data from 74 students who took one of two courses provided provided in two English-related majors: English Education (E-edu) and English Language and Literature (ELL). The survey items included 26 items quantitatively measured on a Likert scale and 3 open questions. The quantitative analysis revealed (1) positive impressions about the E-edu course that provided straightforward contents directly related to the designated textbook; (2) negative ratings for the ELL course that provided intense training with interdisciplinary course contents; (3) more negative ratings for the survey items asking about three educationally associated categories (academic achievement, L2 improvement, and course efficiency), compared to their self-rated effort throughout the semester; and (4) the ELL students’ stronger tendency to rate academic achievement lower relative to their effort. The overall results indicate that the EMI method may not be appropriate for an intense course with academically-driven technical contents, and these trends were confirmed by the qualitative analysis based on the open-question items. We conclude that the efficiency of university-level English-medium courses depends on the complexity and depth of course contents.