Semantic short-term memory (STM) patients have a reduced ability to retain semantic information over brief delays but perform well on other semantic tasks; this pattern suggests damage to a dedicated buffer for semantic information. Alternatively, these difficulties may arise from mild disruption to domain-general semantic processes that have their greatest impact on demanding STM tasks. In this study, mild semantic processing impairments were demonstrated in 2 semantic STM patients. They performed well on untimed semantic tasks but were deficient in accuracy and reaction times on speeded tasks. Demanding semantic production tasks were also affected. These patients were compared with a case series of individuals with semantic aphasia whose multimodal semantic difficulties stemmed from poor cognitive control. STM and semantic performance were more impaired in this group, but there were qualitative similarities to the semantic STM patients. The difference between the 2 patient types may be a matter of degree. In semantic aphasia, severe disruption to semantic control leads to global semantic impairments, whereas in semantic STM milder disruption might impact mainly on STM tests because of the high control demands of these tasks. © 2009 American Psychological Association.