This paper investigated semantic transfer in second language leing and provided studies involving two groups of English as a second language population, Chinese and Korean ESL leers. They were asked to perform a semantic judgment task in which they decided whether or not two English words were related in meaning. Two types of related word pairs were used in studies. One type of word pairs shared same L1 translation and the other type did not share same L1 translation. Both groups of ESL speakers responded to the same-translation pairs significantly faster than to the different-translation pairs. However, no such same-translation effect was found among native speakers of English. The same-translation effect found in L2 speakers have showed that first language semantic structures have significant impacts on L2 lexical representations and L2 processing. Pedagogical implications for L2 vocabulary teaching are discussed.