Semantic retrieval consistently activates left inferior frontal regions, yet lesions to these areas do not typically result in semantic deficits. This discrepancy has led to the hypothesis that left prefrontal areas are primarily involved in executive processes while semantic information is retrieved from temporal cortices. We investigated semantic executive processing by changing, over trials, the semantic association to a stimulus. Using fMRI and PET, we demonstrate that changes in semantic association increased activation in temporal as well as frontal areas. The similar effects in temporal and frontal areas suggest that semantic executive processes are not confined to the left inferior frontal cortex but might be distributed throughout the semantic system.