The aim of this research is to examine the effect of gamified STEM activities on 3rd and 4th grade students' intrinsic motivation, perception of problem-solving skills, and critical thinking disposition. In this mixed method study, problem solving skills perception scale, critical thinking disposition instrument and intrinsic motivation inventory formed the quantitative data, while, activity worksheets, field notes and student interviews, formed the qualitative data. After 8 weeks of implementation, quantitative data were analyzed and significant differences were found between pre-test and post-test results on students' critical thinking disposition level. Although it is not significant, the results showed that an increase was found in students' perception of problem-solving skills. Besides, students' intrinsic motivation levels were found high, as well as students stated that "gamified STEM" activities help them learn and practice the content and they found the activities enjoyable, competitive, and exciting. Moreover, the rewards and badges that they won at the end of the activities were motivating.