The 21st century, marked by digitalization, has had a profound impact on many aspects of life, one of which is education. It takes skills to meet all the challenges and phenomena of globalization in the 21st century. One of the skills that students need to have is critical thinking skills. This research aims to understand the development of learners' critical thinking skills through STEM-based physics learning on gas kinetic theory material. STEM refers to the four fields of science, technology, engineering, and mathematics taught in one discipline. This research uses a problem-based learning model, and every aspect of STEM is integrated into the learning tools used in RPP, UKBM, curriculum materials, and worksheets. The research design was a Quasi-Experimental Design using Nonequivalent Control Group Design. The study subjects were students of class XI MIPA 7 and XI MIPA 6 of SMA Negeri 1 Kendal. The development of critical thinking skills was analyzed based on pretests, posttests, and discussion sheet responses. Research shows that STEM-based learning can develop critical thinking skills in intermediate categories.