Critical thinking skill is one of the skills needed by the graduates of junior high school  to face the industrial era 4.0 . It is a skill in which ones are able to identify problems, find the source of problems, and get the best solution to the problems. Many English teachers at senior high school face problem to teach speaking. Their students only express certain language functions without elaborating the topic. It means that they have not developed critical thinking. The cause of the problem is that the students have limited ideas about the topic they discuss. One of the ways to solve the problem is by selecting the right topics which are in line with the background knowledge of the students. This Lesson Study based research aims at describing and explaining how selecting the right topics for speaking can enhance critical thinking skill of senior high school students.