This research was conducted to design a Problem Based Learning (PBL) based learning module with the ADDIE model. The problems studied are 1) How is the feasibility (validity) and learning effectiveness of the Problem Based Learning (PBL)-based module developed on the buffer solution material to measure students' Higher Order Thinking Skills (HOTS) and 2) What are the students' chemistry learning outcomes using the module-based Problem Based Learning (PBL) is higher than the KKM score. The subjects of this study were 3 expert validators (expert lecturers), and 1 high school chemistry teacher to evaluate the learning to be developed and class XI MIA students of SMA Negeri 1 Purba who were determined by random sampling using an experimental class totaling 30 students. The results of the study showed that 1) the problem-based learning module for chemistry-based learning buffer solution material that was developed was feasible to be used for learning materials to improve students' critical thinking skills. The module is declared effective as seen from the increase in student learning outcomes, namely the average pretest value of 33.5 and posttest 80.13 in the experimental class, 2) The learning outcomes of chemistry using Problem Based Learning (PBL)-based modules developed on buffer solution material are higher than the value KKM (75) with an average score of 80.13.