ABSTRACT Learning using Science Technology Engineering and Mathematics (STEM) can help students solve problems and draw conclusions from previous learning by applying them through science, technology, engineering and mathematics. This study aims to determine the effect of Science Technology Engineering and Mathematics (STEM) approach on students' critical thinking skills in biotechnology major. This type of research is pre-experimental with a One-Group Pretest-Posttest design. The sampling technique used was total sampling with a total of 67 students.from class IX, where indicators of critical thinking are 1) Elementary Clarification, 2) Basic Support, 3) Inference, 4) Advanced Clarification, 5) Strategies and Tactics. Data collection techniques used pretest and posttest instruments, data analysis techniques used the One-Sample Kolmogorov-Smirnov Test with the results of the study showing that there was an increase in pretest and posttest results, namely the average pretest score of 23.03 with an average posttest score of 80 .30 and the average N-Gain is 0.74 in the high category. Based on the results of the hypothesis test, it shows that the significance value is 0.000 where