This study aims to describe the ability to think critically in mathematics through the PBL (Problem Based Learning) model with a STEM (Science, Tecnology, Engineering and Mathematic) approach in terms of the curiosity of grade VIII students. The research method used in this study is a mix method with a sequential explanatory model. The population in this study is grade VIII students of SMP Negeri 2 Sumowono and SMP Islam Sudirman Sumowono for the 2022/2023 school year with samples of grade VIII A and class VIII B from each school as experimental classes and control classes. The data collection techniques used in this study were tests, documentation, questionnaires, observations, questionnaires, and interviews. Quantitative data are tested by mean test, proportion test, mean difference test and proportion difference test, and simple linear regression test while qualitative data with data validity, data reduction, data presentation and drawing conclusions. Students with high curiosity categories are able to solve problems in logical and appropriate steps. Students with curiosity who are able to write down the solution steps quite well, but there are difficulties in completing the final results, while students with low curiosity have not been able to solve problems with the right solving steps because they have not been able to interpret the problem correctly.