We investigated effects of crosslinguistic phonological and semantic similarity on the bilingual lexicon of late unbalanced bilinguals. Our masked priming paradigm used L1 (Russian) words as masked primes and L2 (English) words as targets. The primes and the targets either overlapped – phonologically, semantically, both phonologically and semantically – or did not overlap. Participants maintained the targets in memory and matched them against occasionally presented catch stimuli. N170 and N400 components of the word-elicited high-density ERPs were identified and analysed in signal and source space. Crosslinguistic semantic similarity shortened the reaction times. The semantics-related N400 amplitude difference correlated with individual L2 proficiency, while phonological similarity suppressed the N400 amplitude in the semantically unrelated condition. ERP source analysis suggests that these ERP dynamics are underpinned by cortical generators in the left IFG and the temporal pole. We conclude that the semantic and phonological interplay between L1 and L2 suggest an integrated bilingual lexicon.