This paper examines gender assignment in Spanish–English bilingual speech and develops a theoretical account of gender features in the bilingual grammar on the basis of the linguistic properties that correlate with gender assignment. An analysis of 76 sociolinguistic interviews from an autonomous bilingual community in Southern Arizona, U.S. (Carvalho 2012) reveals three key findings in terms of gender assignment in Spanish Det–English Noun switched DPs (i.e., el industry ‘the.M.SG’): (i) biological sex categorically determines gender assignment with human-denoting nouns; (ii) frequent inanimate nouns that have Spanish feminine counterparts are feminine in bilingual speech; (iii) masculine is a prevailing default gender. Following Kramer’s (2015) proposal of gender features, it is argued that an interpretable [+/-FEM] feature encodes biological sex in the grammar whereby a category-neutral √ combines with a n hosting an interpretable [+/-FEM] feature and triggers feminine (i.e., la coach ‘the.F.SG’) or masculine (i.e., el stepson ‘the.M.SG’) agreement. Inanimate feminine nouns are associated with an uninterpretable [+FEM] feature as the result of bilingualism (i.e., la school ‘the.F.SG’), and masculine default gender is viewed as an effect of Preminger’ (2009) failed Agree. On the basis of these findings, this paper rejects the distinct-lexicons view of the bilingual language faculty (MacSwan 2000 et seq.) and attempts to substantiate a single-lexicon approach compatible with a realizational (Late Insertion) view of the morphosyntactic model (Halle and Marantz 1993).