STEM education has taken on high importance in Hong Kong K-12 education landscape. Despite policy advocacy and curriculum endeavour, the quality of STEM education varies significantly between schools. Research literature indicates that high-quality STEM education requires teachers’ rigorous delivery of topics and appropriate pedagogies, and one approach to improve such practices is teacher professional development (TPD). However, because current research on TPD has not given explicit consideration to the complex nature of STEM education, there remains a lack of a clear blueprint of how TPD should be conducted to build teachers’ capacity for STEM education effectively. This paper presents a case study that explores the necessary attributes and identifies the missing links of STEM education TPD by understanding how various TPD models supported a Hong Kong K-12 school embracing STEM education. Qualitative data collection methods, including semi-structured interviews and classroom observations, were employed to draw a picture of TPD implementations in the selected school. The findings suggest that, at the macro-level, effective STEM TPD should not stop at employing mixed use of TPD models; the models have to be integrated organically with respect to a school-based STEM curriculum implementation approach. A collaborative culture between teachers must be cultivated for effective inter-disciplinary integration. Collaborative action research should also be promoted to develop collective wisdom of STEM pedagogies. At the micro-level, TPACK and cross-disciplinary integration skills need to be focusing areas of STEM TPD. With these guiding principles, some possible strategies for effective STEM education TPD are suggested. Copyright © 2023 The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.