The need to benefit from information technologies in the twenty-first century digital age is increasing in all economies to overcome problems and difficulties and to have desired solutions. So, developing algorithmic thinking has been important as a skill that requires the application of knowledge from different disciplines, especially science, technology, engineering and mathematics, and improves solving real life problems. Therefore, there is a need for practical studies on how to develop algorithmic thinking and what kind of activities and learning content can be used in classrooms. The effect of STEM-focused physical computing activities with Arduino on algorithmic thinking skills and STEM awareness of teacher candidates was investigated by mixed-method research. In addition, student-teacher roles in the activities and the advantages-disadvantages of the activities were discussed by considering the views of the teacher candidates. The study group of the research consists of twenty-four volunteer students. They were selected by purposive sampling method, and they are studying in the last year of science teaching undergraduate program at twelve different universities in Turkey. The findings showed that STEM-focused physical computing activities developed teacher candidates' algorithmic thinking skills. Therefore, it can be said that the activities increased the awareness of teacher candidates about STEM. The effect size (Cohen d) of the STEM awareness scale was calculated as 0.98 according to the pre-test and post-test averages.