Presenting semantically related L2 words is a popular method in EFL coursebooks, but the research results on this issue remain inconclusive. Therefore, this study aims to investigate the effects of semantic clustering on Korean young learners’ English vocabulary learning. The study was conducted with 174 primary school students. The subjects were divided into two groups: a semantically related words group (SR) and a semantically unrelated words group (SU). For the six weeks of treatment, the two comparison groups were taught the same 40 vocabulary items in different clusters. The vocabulary test results showed that both vocabulary presentation methods had a positive effect on vocabulary learning. However, the SU group significantly outperformed the SR group. These findings indicate that presenting new L2 words in semantically unrelated sets might be more effective than semantically related sets.