STEM, STEAM education is important for building a better future, and teachers have a key role in attracting students to the field of STEM. However, when teachers need to shift from traditional disciplinary-based education to integrated STEM education, they often find this transition challenging. This difficulty arises because their beliefs about science teaching and learning are deeply rooted in traditional disciplinary-based approaches. Beliefs have a profound influence on their teaching practises as well as their professional development, even though teachers are often not conscious of their own beliefs. To address this issue, we employed a phenomenological approach to investigate the phenomena when their beliefs espoused by asking formative episodes that influenced their development as science teachers. This study aimed at exploring the current subject-specific beliefs of in-service science teachers. This told us how best to guide teachers through this process of the transition from traditional disciplinary-based education to STEM education. Our findings revealed that teachers' beliefs showed that curiosity and/or interest towards science to be the most important factors in student learning. This indicates that while teachers' core beliefs are not entirely disciplinary-oriented, they are more open. It would reduce their anxiety and low self-efficacy in conveying STEM education.