In language teaching, speaking is one of the complex skills that need to be developed specifically. However, how to teach speaking skills is an ongoing debate. The aim of this study is to examine the effect of STEM-based activities on the development of speaking skills of students in secondary schools. The study was conducted in a secondary school in Uralsk, Kazakhstan in 2022. In the study designed according to the control group pretest-posttest design, STEM activities in the experimental group and traditional teaching practices in the control group were carried out. The pretest-posttest and experimental application of the study was carried out with 60 students, 30 experimental and 30 control groups. As a result of the 6-week experimental applications, it was found that STEM-based activities in the experimental group increased students' speaking skills compared to traditional teaching. In addition, as a result of the experimental applications, it was observed that STEM-based activities increased students' attitudes towards language lessons and speaking skills at a positive and high level.