Challenges and demands of the 21st century occur, among others, in the learning process and student competence. One way to achieve the 21st century learning goals in the 2013 curriculum and independent curriculum is through the development of teaching materials. The development of STEM-based science teaching materials can strengthen critical and creative thinking skills in elementary schools. R&D development research uses the ADDIE Model (Analysis, Design, Development, Implementation, and Evaluation). The data used are qualitative and quantitative. Collecting data using interviews, questionnaires, validation sheets, and documentation with descriptive analysis techniques. The results of expert validation were obtained from 85% material expert validation, 84% media expert validation. The results of student responses are 95% and educator responses are 92%. The effectiveness of the use of teaching materials was measured based on the n-Gain test results and t-test. The results showed that the use of STEM-based science teaching materials was quite effective in strengthening critical and creative thinking skills, as evidenced by the n-Gain of the experimental class (0.37) higher and significantly different compared to the control class (0.22).