Inhibition of automatic semantic processing was examined in children who have high functioning-pervasive developmental disorders (HF-PDD) with or without reading difficulty and in typically developing children. In Experiment 1, lexical decision tasks were conducted under three priming conditions: (1) normal character condition, (2) transposed-letter internal nonwords condition, and (3) transposed-letter external nonwords condition. The results indicated that all participants displayed semantic priming under the normal and transposed-letter internal nonwords condition, whereas semantic priming was not observed under the transposed-letter external nonwords condition. In Experiment 2, speed-reading was conducted under normal, transposed-letter internal nonwords, transposed-letter external nonwords condition, and nonword conditions. The results indicated that HF-PDD students with reading difficulty showed low reading scores under the nonword condition. Moreover, their reading score under the transposed-letter internal nonwords condition declined more than that under the nonword condition. The above results indicate that students with HF-PDD and reading difficulty have problems in conducting bottom-up processing while inhibiting top-down processing, when automatically generated semantic processing interferes with the processing conducted through the phonological route.