Alkylsilane-based self-assembled monolayer films were prepared on n-Si with a thin oxide (nominally SiO2) layer. The surface morphology was characterized by atomic force microscopy (AFM). Photocurrents between the n-Si and a redox species in liquid solution were also examined as a function of the alkane chain length of the self-assembled monolayer (SAM) molecules. They demonstrate that the films are compact and that current flow is blocked by the alkane monolayer, displaying a significant decrease with increasing chain length of the alkane.