Semantic integration and working memory both decline with age. However, it remains unclear whether the semantic integration decline is independent of working memory decline or whether it can be solely explained by the latter factor. In this event-related potentials experiment, 43 younger adults and 43 cognitively healthy older adults read semantically congruent and incongruent sentences. After controlling for working memory, behavioral accuracy was significantly lower in the older adults than in the younger adults. In addition, the semantic integration related N400 effect (incongruent vs. congruent) for correct trials was apparent in the whole brain in the younger adults but restricted to the posterior region in the older adults. The results clarify the relationship between working memory and semantic integration, and clearly demonstrate that semantic integration decline is independent of working memory decline during aging.