We demonstrate facile polymer gate dielectric surface-modification method for organic thin-film transistors. We introduce self-assembled surfactant layer onto the top surface of PVP dielectric. The surfactant-modified PVP acquires merits compared to pristine PVP in terms of surface smoothness and hydrophobicity. X-ray study supports the superiority of surfactant-modified PVP and proved the tendency of agglomeration of semiconductor. The surfactant-modified PVP show overall ascendency over the OTFT with pristine PVP in terms of hysteresis and reliability.