In this study we present the opinion of 114 Bulgarian teachers in STEM (mathematics, physics, chemistry and technology and entrepreneurship) concerning the barriers in using educational computer games in their teaching practice. There are various obstacles in the process of using educational computer games. They are associated with a high cost of existing educational games, the provision of content-quality games, technical equipment, the need for additional teacher training for the use of educational computer games, a time constraint within the classroom, the lack of match of curriculum games. We analyze the teachers' opinions with relevance to existing school policies for use of educational computer games, experience in use of educational computer games, teaching experience, age, school subject and school level - primary, low secondary or upper secondary school.