Our ability to effectively retrieve complex semantic knowledge meaningfully impacts our daily lives, yet the neural processes that underly successful access and transient failures in access remain only partially understood. In this fMRI study, we contrast activation during successful semantic access, unsuccessful semantic access because of transient access failures (i.e., “tip-of-the-tongue,” “feeling-of-knowing”), and trials where the semantic knowledge was not possessed. Twenty-four human participants (14 female) were presented 240 trivia-based questions relating to person, place, object, or scholastic knowledge domains. Analyses of the recall event indicated a relatively greater role of a dorsomedial section of the prefrontal cortex in unsuccessful semantic access and relatively greater recruitment of the pars orbitalis of the inferior frontal gyrus in successful access. Successful access was also associated with increased activation in knowledge domain-selective areas. Generally, knowledge domain-selec...