The purpose of this study was to analyze the effectiveness of STEM-PjBL learning on students' critical thinking, creative thinking, communication, and collaboration (4C) skills. This research is quantitative with a one-group pretest-posttest design. The research samples were 106 class XI State Senior High School 16 Semarang students. Quantitative data on critical thinking skills were analyzed using the N-gain test, while other data were analyzed descriptively. The results showed increased students' critical thinking skills based on the N-gain test. The paired sample t-test results in the SPSS 28 program obtained a significance value/Sig. (2-tailed) of 0.001, there were differences in critical thinking skills before and after STEM-PjBL learning. STEM-PjBL learning effectively trained students' creative, collaborative, and communicative thinking skills with high categories. This learning effectively trained students' critical thinking, creative thinking, communication, and collaboration skills

The study aims to describe the validity, applicability, and effectiveness of the developed learning aids. This research is a research and development (RD) research that uses the Borg and Gall model. The subjects of the wide-scale trial were 106 students of class XI at SMAN 16 Semarang. The data analysis used was descriptive percentages.  The results and conclusions of this study indicate that: (1) overall learning aids are highly valid based on expert validation, and construct validity, especially for tests of critical thinking skills obtained valid and reliable results (2) learning aids are well implemented; (3) learning aids effectively improve students' critical thinking skills with 75% of students meeting the minimum completion criteria, and regarding N-gain test, there is an increase in critical thinking skills with moderate criteria.  The STEM-PjBL Learning aids effectively trains the ability to think creatively, communicatively and collaboratively with high criteria.