Students can receive STEM education based on an efficient and effective interdisciplinary approach naturally depending on the teachers’ ability to relate their major to the knowledge and skills from other disciplines (Nadelson et al., 2013). According to Osborne et al. (2003), the quality of a teacher constitutes the most important factor in students’ maintaining their career choice in STEM areas. However, as teachers are not often encouraged to relate their subject area to other disciplines, they just try to convey information to learners about their respective subjects, not attaching much importance to the extent to which knowledge and skills learned in these courses are applied to other courses or how they are associated with other courses. Wang et al. (2011) argue that one of the major educational problems of the K-12 STEM education is the minimum amount of professional programs to guide or help teachers about the relationship among STEM disciplines and how to teach this relationship in the class. Research results about effectiveness of the STEM teaching curricula also support the above mentioned case. Researches demonstrate a number of obstacles to teachers’ inability to associate their own fields with other areas (natural sciences, math, technology and engineering fields). These include a reluctant co-operation with teachers in other disciplines, teachers’ inadequate information about effects of the STEM approach, teachers’ not seeing the STEM approach as a method to increase students’ achievement in their discipline, school’s structural limitations, shortage of educational materials and so on (Pinell et al., 2013; Raju and Clayson, 2010; Nadelson et al., 2013; Shahali et al., 2015; Han et al., 2015; Siew et al., 2015). The result revealed that teachers learn more about the relationship among sciences, technology, engineering and mathematics disciplines, integrated STEM instructional strategies and STEM concepts, they feel more comfortable in teaching STEM (Nadelson et al., 2012; Stohlmann et al., 2013; Halim et al., 2014; ). A professional development workshop approach for pre-service and in-service teachers is one way of creating teachers’ awareness of science teaching through a STEM approach (Han et al., 2015). In this regard, the present study intends to reveal the changes in science teachers’ perception of STEM approach as a result of the STEM education program developed for them. STEM in-Service Programme is a short-term (five day) Professional development programme aimed to increase STEM teachers’ abilities to teach integrated STEM education and to increase their beliefs and attitudes of STEM approach. We invited 21 science teacher as volunteering. The STEM programme was held from 15 to 19 February 2016 in Recep Tayyip Erdoğan University Education Faculty, Rize. The training provided instructional strategies to aid facilitators in implementing STEM instruction and increase their understanding of the connection between the areas of STEM and to explore mechanisms for integration across STEM disciplines. Participants were divided in four separated workshop named Da Vinci, Dynamic, Pinomatik, and Robotic. The activities in the workshops were using Engineering Design Process (EDP) as a bridge to connect STEM subjects together. Participants were exposed to Engineering instruction as an instructional strategy that integrates STEM contents. Key Words: in-Service education, STEM approach, Science teachers