This study utilizes a concept mapping method to explore the underlying structure and dimensionality of Korean student teachers' autobiographical reflections on their professional identity formation. Participants consist of 90 students enrolled in bachelor's and master's degree programs in English teacher education. The study results imply core concepts (backgrounds for career pursuit, conceptualizations of a good English teacher/teaching, and confidence/aspirations) that constitute professional identity development of Korean EFL student teachers. Dimensionality analysis suggests that the impetus for guiding student teachers' professional development is their knowledge and experiences related to teacher qualities and teaching practices.