This study investigated the effect of semantic inconsistency of roots on morphological processing to explore the development of morphological representations within the mental lexicon. We examined masked priming of Hebrew words of changing semantic transparency at two reading levels. The results revealed a disparity in the performance of fourth graders and seventh graders, suggesting that morphological representations within the mental lexicon of more skilled readers become abstract and depend more on the formal morphological structure of the root rather than its semantic properties. The results suggest a gradual development of generalized morphological representations in the mental lexicon. (Contains 2 tables.)