STEM-based learning stands out as an important approach in developing students' attitudes toward STEM fields and their perceptions of self-efficacy. The aim of this research was to examine the attitudes of vocational upper-secondary school students toward STEM-based learning and their perceptions of STEM self-efficacy in vocational workshop classes. The research was conducted using a weak experimental design with a single group pre-test and post-test in the 2023–2024 academic year with 30 ninth-grade students studying in the field of Electrical-Electronics Technology at a vocational and technical secondary school in Türkiye. The data were collected through the STEM Attitude Scale and the STEM Self-Efficacy Scale administered before and after the four-week STEM-based teaching application. Descriptive statistics, paired sample t-test, and Pearson correlation analysis were used in the data analysis. The findings showed that the STEM-based teaching practice was associated with positive changes in students' attitudes toward STEM and their perceptions of STEM self-efficacy. Additionally, a statistically significant and positive relationship was identified between students' attitudes toward STEM and their perceptions of STEM self-efficacy. In conclusion the findings suggest that the integration of STEM-based learning into vocational workshop courses can support students' attitudes toward STEM and their perceptions of self-efficacy.