This study aims to improve students' thinking skills by developing a learning tool that can improve the critical thinking skills of vocational students using the guided inquiry model. This guided inquiry model was chosen based on the process. This model is able to provide opportunities for teachers to explore critical thinking skills in students. Students learn to apply the process by carrying out problem-based investigations designed to learn science concepts. This research uses the Tessmer development model. The subjects of this research were 3 expert lecturers, the individual trial subjects were 3 students with different academic abilities, the small group trial subjects were 10th grade students with 6 students, the field trial subjects conducted on 10th grade students who numbered 23 people. There are three types of data obtained in this research, namely validity data, practicality data, and effectiveness data. The results of this study are valid learning tools because all components of learning tools are developed in accordance with the guiding principles of development and have been validated by experts. Learning tools are also classified as practical because they are easily implemented and implemented by the teacher in the learning process and get a good response from students. The resulting learning tool is quite effective because the results of students' thinking skills are classified as good, cognitive learning outcomes are classified as good.