Associating a content word to its rational semantic relations is regarded as a language learning strategy which explicitly contributes to mental lexicon. Semantic mapping herein seems to constitute an efficacious pattern for its practice in language instruction. Conversely, it appears to be among the least frequently used vocabulary learning strategies in language classrooms. This study points at semantic mapping as a practice for EFL learners by suggesting its pros and cons, and thus aims to raise awareness with this respect. The samples for the treatment of the study involve 20 EFL students studying at a state university in Turkey. A second group of the same size was randomly chosen as the control group from the same accessible population. All the participants were subject to a pre-test and a post-test measuring the size of the vocabulary known. The findings indicate a significant increase in the vocabulary size of the treatment group, surpassing the average size of undergraduate non-native speakers of English from non-European background.