Field-effect transistors (FETs) with thin films of C-60 have been fabricated with Au electrodes modified by a series of 1-alkanethiols. All C-60 FETs show n-channels of normal FET properties. It has been found that the output properties for the FETs with the Au electrodes modified by 1-alkanethiols with long alkyl chains are largely affected by the carrier-injection barrier (i.e., the current vs drain/source voltage plots exhibited concave-up nonlinearity at low voltage regions). The output properties are substantially dominated by an additional tunneling barrier of 1-alkanethiols inserted into the junction of the Au electrode and C-60 thin films, and the parameters associated with the junction barrier height and tunneling efficiency were determined from the output properties based on the thermionic emission model for double Schottky barriers.