By preparing phenyl-terminated monolayers on hydrogen-terminated silicon (111), we show that their higher surface densities in comparison with n-alkyl monolayers improves their electrical properties (lower reverse-bias currents, higher effective barrier heights, and closer-to-unity ideality factors) when contacted using either mercury drop or thermally deposited gold electrodes. Consistent with these macroscopic results, the ballistic electron emission microscopy characterization shows a significant decrease in ballistic current and higher local barrier height for the phenyl-terminated monolayers, when compared with gold | n-alkyl monolayer | silicon junctions. We propose that increased intermolecular interaction through π–π stacking of the phenyl head-groups stabilizes the monolayer structure at the buried interface and inhibits the penetration of thermally deposited gold atoms.