This study investigates how fluent second-language (L2) learners of English produce and perceive the /æ/–/ɑ/ vowel contrast of Southwestern American English. Two learner groups are examined: (1) early, proficient English speakers who were raised by Spanish-speaking families but who became dominant in English during childhood and, as adults, lack communicative abilities in Spanish, and (2) Spanish-speaking late learners of English who continue to be dominant in Spanish. The participants provided data in three tasks: one production and two perceptual. The study finds that both learner groups differ from native controls in their production and perception of the /æ/–/ɑ/ contrast. The findings shed light on our understanding of the relative effects of age (at onset of language exposure) and language dominance (at time of testing) by showing that sequential bilingualism impacts phonetic behavior even when speakers have become dominant in the target language.