Determination of integrated STEM teacher competencies for the effective use of STEM education is important in terms of managing the learning process and performing STEM integration effectively. More studies are needed to identify and describe STEM teacher competencies as a result of comprehensive research. The purpose of this research was to constitute integrated STEM teacher competencies for secondary education by taking the opinions of the STEM experts. The research was carried out via threeround modified Delphi method and validation stage. The following four competency areas were defined within the scope of integrated STEM teacher conceptual framework: Cognitive Characteristics in STEM Teaching, STEM Teaching Skills, Affective-Motivational Characteristics in STEM Teaching, and Collaboration and Engagement Skills. Under these competency areas, 14 competencies and 58 competence indicators were determined. This study would be a guiding framework for the development of STEM teacher education programs at the undergraduate or graduate levels.