For the advancement of current and future economic and overall well-being to occur, STEM professionals are highly needed. STEM education is an approach that integrates science, technology, engineering and mathematics curricula into one interdisciplinary curriculum. In the context of STEM education, learners acquire deep and critical thinking abilities, which help them become creative and analytic thinkers, and hence innovators in their careers. For this to happen, the teacher must be trained to successfully design and effectively teach an integrated STEM curriculum. The purpose of this study was to analyze Saudi Arabian science and mathematics teachers' attitudes toward integrating Science, Technology, Engineering and Mathematics (STEM) in teaching before and after they participated in a short professional development program focused on STEM integration in a specific middle school science and mathematics content. The participants were 48 Saudi Arabian science and mathematics teachers, who participated in a 6-day program held in Riyadh, Saudi Arabia. The research methodology was a pretest-posttest one group (pre-experimental) design. The primary data source was the Instrument for Teachers' Attitudes Toward Teaching Integrated STEM. The results indicate that Saudi Arabian science and mathematics teachers' perceptions of difficulties decreased due to their participation in the professional development program on integrated STEM. Meanwhile, the teachers' self-efficacy improved following their participation in the STEM professional development (PD) program. However, no perceived effect was found for the teachers' perceptions of the relevance of or their anxiety about or enjoyment of Integrated STEM teaching due to their participation in the 6-day PD program. We argue that Engaging teachers in integrated STEM professional development may improve their attitudes toward and increase their interest in teaching this approach. To improve teachers' attitudes toward, it is suggested that future PD programs should be long and continuous, and focus on training science and mathematics teachers to teach integrated STEM subjects.