This study explores the development of professionalism in using Educational Technology (EdTech) among Korean elementary English teachers amid the increasing integration of technology in English education. Employing the Grounded Theory methodology, the study involved in-depth interviews with nine Korean elementary English teachers experienced in using EdTech. It aims to identify their EdTech experiences, the elements constituting EdTech professionalism, and its developmental process. The study reveals that teachers' EdTech professionalism encompasses a proactive approach towards technology, continuous professional growth based on practice and reflection, and adaptation of teaching methods in response to evolving technologies and learner needs. It highlights the importance of teachers' self-directed approach, collaboration with other teachers, and the integration of pedagogical, content, and technological knowledge into their English teaching. The findings have implications for teacher education and the advancement of EdTech-utilized English education, suggesting new processes and directions for developing elementary English teachers' professionalism in the rapidly evolving landscape of educational technology.