This study investigates two models of L2 vocabulary acquisition at an advanced L2 level: L1 lemma mediation and the revised hierarchical models. Proponents of the L1 lemma mediation model postulate that advanced L2 learners map L2 words to L1 meanings or concepts, whereas proponents of the revised hierarchical model argue that the increasing experience in L2 helps learners remap the L2 words to their L2 meanings. In this study, 26 proficient Arab L2 speakers of English and 26 English native speakers were given 76 semantically related word pairs and were instructed to rate their semantic relatedness on a 5-point Likert scale as quickly as possible. It was found that word pairs sharing the same Arabic translations had been rated significantly higher than word pairs not sharing the same Arabic translations. The results supported the L1 lemma model--namely, even advanced L2 learners still rely on their L1 to access the meanings of L2 words.