Ida Rosdiyanti. 2026. Development of a Problem-Based Learning (PBL)-Based E-modul to Improve Junior Higher School Students' Higher Order Thinking Skills (HOTS) on the Topic of Work and Energy. Thesis. Supervisor I: Prof. Sulistyo Saputro, M.Si., Ph.D. Supervisor II: Prof. Dr. Harlita, S.Si., M.Si. Master's Program in Science Education, Faculty of Teacher Training and Education, Universitas Sebelas Maret, Surakarta.ABSTRACTThe low level of Higher Order Thinking Skills (HOTS) among junior higher school students is partly attributed to instructional materials that inadequately support higher-order thinking. Existing e-moduls are generally conventional and have not integrated the syntax of Problem-Based Learning (PBL), which promotes critical thinking and problem-solving skills. This study aimed to develop a PBL-based e-modul on the topic of Work and Energy, evaluate its feasibility, and examine its effectiveness in improving students' HOTS.This study employed a Research and Development (R&D) approach using the Four-D (4D) model consisting of Define, Design, Develop, and Disseminate stages. The developed product was validated by two expert lecturers and four science teachers using Aiken's V analysis. Its effectiveness was evaluated through a pretest-posttest control group design involving Grade VIII students at SMP Negeri 2 Karanganyar. Data were analyzed using the Wilcoxon signed-rank test, the Mann–Whitney U test, and normalized gain (N-Gain).The results indicated that the developed e-modul met the criteria of validity and feasibility, with excellent validity in terms of content, language, media, and PBL implementation. Student readability responses also showed that the e-modul was appropriate for classroom use. Furthermore, the PBL-based e-modul effectively improved students' HOTS, as indicated by higher N-Gain scores in the experimental class than in the control class and statistically significant differences between the two groups (p < 0.05).In conclusion, the developed PBL-based e-modul is valid, feasible, and effective for improving junior higher school students' Higher Order Thinking Skills on the topic of Work and Energy.