Field-effect transistors (FETs) with thin films of C60 have been fabricated with Au electrodes modified by aseries of 1-alkanethiols. All C60 FETs show n-channels of normal FET properties. It has been found that theoutput properties for the FETs with the Au electrodes modified by 1-alkanethiols with long alkyl chains arelargely 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 additionaltunneling barrier of 1-alkanethiols inserted into the junction of the Au electrode and C60 thin films, and theparameters associated with the junction barrier height and tunneling efficiency were determined from theoutput properties based on the thermionic emission model for double Schottky barriers.