Armelia Pati Raja Pengarang SELFIANA P MBADI Dosen Pembimbing 2 Alexander H. Kabelen Dosen Pembimbing 1 Alexander Home Kabelen Penguji 1 Novriani Rabeka Manafe Ketua Penguji SELFIANA P MBADI Penguji 2

This study was conducted to answer two research questions, namely how the Hidden Word Puzzle Game technique was implemented in teaching vocabulary to the eleventh-grade students of SMAN 6 Kupang and whether the technique was effective in improving their vocabulary mastery in the academic year 2025/2026. The researcher used a quantitative method with a quasi-experimental design involving an experimental group and a control group, each consisting of 11 students selected from the eleventh grade. The main instrument used in this study was a vocabulary test, which was given in the form of a pre-test and a post-test to measure the students’ vocabulary mastery before and after the treatment. The experimental group was taught by using the Hidden Word Puzzle Game, while the control group was taught by using the conventional teaching method. The statistical hypothesis of this study stated that the Hidden Word Puzzle Game had a significant effect on students’ vocabulary mastery, while the null hypothesis stated that there was no significant effect. The findings showed that both groups experienced improvement, but the experimental group obtained better results than the control group. The mean score of the experimental group increased from 52.27 in the pre-test to 75.91 in the post-test, while the control group increased from 50.45 to 67.73. In addition, the effect size analysis showed a Cohen’s d value of 1.15, which was categorized as a strong effect, indicating that the difference between the two groups was not only statistically visible but also practically meaningful. Based on these findings, it can be concluded that the Hidden Word Puzzle Game is effective in improving vocabulary mastery, and it can be used as an alternative technique in teaching English vocabulary because it helps students learn in a more active, enjoyable, and effective way.