The effects of aromatic molecular size on the electronic properties of carbonaceous materials were studied using materials extracted from a petroleum pitch. Structural analysis using the combined data of elemental analysis and 'H-NMR revealed that the solvent-extraction technique successfully gave fractions with different size of aromatic systems. Optical band gaps calculated from the absorption spectra of the extracted carbonaceous materials showed a strong correlation with the aromatic molecular size. Junctions between the materials and n-type silicon were prepared by a spin-coating technique of pyridine solutions of the components. They were subjected to photocurrent measurement with infrared light (i= 940 nm). The following results were obtained: (1) the photocurrent depended on the thickness of the extracted carbonaceous film on the n-Si substrate, (2) the junction with a closer optical band-gap energy to the photon energy showed a large photocurrent, (3) no photocurrent was observed for junctions made with silicon pre-cleaned by hydrofluoric acid. Photocarrier generation was concluded to take place near the interface between the film and the n-Si substrate. Carbonaceous film/oxide/n-Si was essential for the photoresponse of those junctions. The solvent-extraction technique is a promising way to obtain carbonbased material with suitable electronic properties.