This study aims to develop an instructional material by discovery model with a cognitive conflict approach that has a positive impact on students' critical thinking skills, especially on temperature and heat material. The development of these instructional materials adapted the 4D (define, design, develop, and disseminate). Teaching materials that have been developed consist of the syllabus, lesson plans, student worksheets, learning materials, and research instruments. The research instrument is an essay test to measure students' critical thinking skills. This product was validated by three expert validators and obtained very high validity criteria. The practicality test was done by observing the implementation of learning accompanied by the questionnaire responses of teachers and students and produces very high practicality criteria. The final value of critical thinking skills students also has high criteria. Therefore, the product developed can be declared valid, practical, and has a positive impact on students' critical thinking skills.