Charge transport through single dibenzo[a,j]coronene (C₃₂H₁₆) molecules (DBC) chemisorbed on the Si(001)-2 × 1 surface was investigated by current-voltage (I-V) measurement with scanning tunneling microscopy (STM) at 25°C. The I-V curves taken from two different adsorption structures of the DBC are found to be significantly different. The major DBC species shows periodic steps in the {I-V} curve, as expected from a possible Coulomb blockade, while the minor DBC species shows a similar I-V curve to the Si substrate. This indicates that the adsorption structure of the chemisorbed DBC molecule to the Si surface governs its conductivity behavior. [DOI: 10.1380/ejssnt.2006.588]