This paper denotes the findings from an action research project, which applied problem-based learning (PBL) in linguistics courses in an MA TESOL program in Vietnam. The project aimed to study the extent to which the use of problem-based tasks in semantic courses could promote students' employment of higher-order thinking skills in their learning. It was found that the PBL approach was specifically appropriate in promoting higher-order thinking skills for students with passive learning habits in such Confucian heritage cultures as Vietnam. With well-designed problem-based tasks and adequate tutoring, students learned how to use higher-order thinking skills to facilitate their learning; how to stay more focused on the completion process of problem-based tasks; and how to be motivated to engage in learning activities. In addition, some students were encouraged to follow the same PBL approach in their own teaching practice. Problem-based tasks which took place at a fixed time during class seemed to cause students to lose interest. In addition, a lack of adequate job experience might also have limited the effectiveness and overall success of the problem-based tasks.