A novel self-assembled monolayer (SAM) on AlO_y/TiO_x is terminated with cyclohexyl groups, an unprecedented terminal group for all kinds of SAMs. The SAM-modified AlO_y/TiO_x functions as a general dielectric, enabling organic thin-film transistors with a field-effect mobility higher than 5 cm² V^-1 s^-1 for both holes and electrons, good air stability with low operating voltage, and general applicability to solution-processed and vacuum-deposited n-type and p-type organic semiconductors.