The present research explores whether obtaining semantic negative priming from a single ignored word depends on whether that word is either consciously or unconsciously perceived. On each trial a prime word was briefly displayed and followed either immediately or after a delay by a pattern mask. The mask offset was followed by a probe display containing a single target word that participants were required to either categorize or identify. Participants were instructed to attend to the target while ignoring the prime word. On half of trials the prime-target pairs were highly associated words belonging to the same semantic category, whereas on the remaining half they belonged to different semantic categories. A differential priming pattern as a function of the masking condition was found: Semantic negative priming when the mask presentation was delayed, and positive priming when the prime word was immediately masked, thus preventing its conscious identification. These results suggest that masking type, which supposedly affects prime awareness, would be a critical factor to obtain negative semantic priming from single words. They also provide evidence that perceiving a stimulus with or without awareness can lead to qualitatively different behavioral consequences, which reflect the contribution of controlled and automatic components, respectively.