Abstract Language production ultimately aims to convey meaning. Yet, words differ widely in the richness and density of their semantic representations and these differences impact conceptual and lexical processes during speech planning. Here, we replicate the recent finding that semantic richness, measured as the number of associated semantic features according to semantic feature production norms, facilitates object naming, while intercorrelational semantic feature density, measured as the degree of intercorrelation of a concept’s features, has an inhibitory influence, and investigate the electrophysiological correlates of the obtained effects. Both the facilitatory effect of high semantic richness and the inhibitory influence of high feature density were reflected in an increased posterior positivity starting at about 250 ms, in line with previous reports of posterior positivities in paradigms employing contextual manipulations to induce semantic interference during language production. Furthermore, amplitudes at the same posterior electrode sites were positively correlated with object naming times between about 230 and 380 ms. The observed effects follow naturally from the assumption of conceptual facilitation and simultaneous lexical competition, and are difficult to explain by language production theories dismissing lexical competition.