The goal of the present study was to examine whether cross-language activation of a bilingual’s native language influences the processing of lexical ambiguity within a second language. Highly proficient Spanish-English bilinguals performed a semantic verification task in which sentence frames were followed by the presentation of the final word of the sentence (the prime word). Participants then decided whether a follow-up target word was related to the meaning of the sentence. On critical trials the sentences ended in a semantically ambiguous word that was either a cognate with Spanish (e.g., novel), or a noncognate control matched on frequency and length (e.g., fast). The preceding sentence context biased the subordinate meaning (e.g., “new”; “refrain from eating”) and targets were related to the irrelevant, dominant meaning (e.g., “BOOK”; “SPEED”). Mean reaction times and error rates were greater when the prime words were ambiguous cognates than when they were ambiguous noncognates. This suggests that the semantic representations from the native language were coactivated and increased the lexical competition from the shared, dominant meaning. Implications for second language vocabulary acquisition and current models of reading are discussed.