The implications of how teacher development courses (TDCs) should be designed for integrated STEM education are essential for in-class STEM education practices. This study compares the three TDCs accomplished to support teachers' professional development (PD) for integrated STEM education in terms of pedagogical knowledge, technological knowledge, and strategy. A holistic multiple-case study design was used in this study. Each TDC was considered a case study, and case-specific analyses were made. The findings obtained for each case were then compared. The first TDC included only computer science teachers and showed us the necessity of interdisciplinary work to enhance integrated STEM education. The second TDC demonstrated that this work could be accomplished by combining the content knowledge of teachers from various disciplines; however, the second TDC's drawbacks included identifying real-world problems, a lack of response to the engineering approach for science and mathematics teachers, and the rigidity of the collaborative working strategy. Then, we focused on the role and purpose of "T"echnology. Finally, we gave the teachers learning tasks to work collaboratively with teachers in their disciplines first and teachers from other disciplines later. This study shows how a TDC should be designed effectively to support teachers' PD for integrated STEM education.