The aim of this study was to develop the STEM Pedagogical Content Knowledge Scale (STEMPCK Scale). Exploratory and confirmatory factor analyses were conducted to examine the structural validity of the scale. Exploratory factor analysis of the scale was conducted using data from 443 preservice teachers who were studying to become science teachers, preschool teachers, elementary school teachers, and mathematics teachers. The confirmatory factor analysis of the scale was conducted using data from 212 students who were enrolled in the same departments. The scale was administered to 655 preservice teachers in total. To determine the reliability of the scale, the Cronbach's Alpha internal consistency coefficient, the corrected total item correlation, and the significance of the differences between the item averages of the top 27% and bottom 27% were examined by t-test. According to the results obtained, the STEMPCK Scale consists of six factors: 21st-Century Skills, Pedagogical Knowledge, Mathematics, Science, Engineering, and Technology. The scale included 56 items. The Cronbach's Alpha values of the factors ranged from 0.878 to 0.90, and the corrected item total score correlations ranged from 0.306 to 0.895. The results of the t-test showed that all the differences between the mean scores of the top 27% and bottom 27% on the items were significant. The results of the analyses indicate that the instrument has reasonable internal consistency and that the theoretical structure was supported by empirical data. These results indicate that the STEMPCK Scale is an appropriate tool for measuring preservice teachers' STEM pedagogical content knowledge. Implications and suggestions for further studies are included.Scientific and technological progress requires workers to have different skills than in the past. In addition to foundational skills like literacy and numeracy, they need competencies such as problem solving, critical thinking, creativity, and collaboration and character qualities such as curiosity. To teach the skills that meet the needs of a 21st-century marketplace, countries have made reforms in their educational systems (Drew, 2011). Science, technology, engineering, and mathematics (STEM) lie at the heart of these reform movements. Through the integration of science, technology, engineering, and mathematics, students would be able to study the challenges that arise in today's world such as energy shortages, environmental problems, and health problems (Bybee, 2010). Students fully equipped with STEM knowledge will be able to identify, apply, and integrate its concepts to understand complex problems and generate solutions to solve those