Hydrophobic self-assembled monolayers (SAMs) with alkyl chains of various lengths were inserted between CVD-grown graphene layers and their SiO2 substrates (figure). As the SAM alkyl chain length increased, substrate-induced doping was suppressed by the ordered close-packed structure of SAMs with long alkyl chains. Accordingly, graphene transistors constructed on SAMs with long alkyl chains exhibited higher electron/hole mobilities with lower Dirac point voltages.