The development of STEM education requires teachers to have knowledge in science and mathematics, comprehensive interdisciplinary knowledge, and the ability to integrate various fields of science, technology, and engineering into the educational process. That calls for new approaches to building teachers' readiness that involve the development of cognitive abilities, including the ability to analyze and critically think creativity, and the ability to innovate. In the article, we present a brief theoretical analysis of scientific sources of domestic and foreign scholars, which allowed us to clarify the concept of "readiness of teachers of natural and mathematical disciplines to use STEM technologies in their professional activities." Considering the approaches to determining the readiness criteria, the criteria are formulated, among which we single out the cognitive criterion, which characterizes the totality of knowledge and ideas about the nature of professional activity, professional knowledge, skills, and abilities to implement STEM in the educational process. The indicators of the cognitive criterion are highlighted: 1) "awareness in the field of STEM," which reflects the level of knowledge of the future teacher about current trends in the development of STEM education and technologies used in STEM projects; 2) "comprehensive interdisciplinary knowledge," which reflects knowledge of various disciplines of the natural and mathematical cycle, as well as an understanding of interdisciplinary connections within STEM and the ability of the future teacher to make connections. The methods of calculating indicators for determining the readiness levels of teachers of natural and mathematical disciplines to use STEM technologies in their professional activities are described. The results of the pedagogical experiment, which was processed according to the Student's criterion, are presented. It has been confirmed that the level of formation of the knowledge component of readiness according to the indicators of the cognitive criterion (awareness of STEM and the availability of comprehensive interdisciplinary knowledge) has positive dynamics in the experimental group.