We have studied the capacitance–voltage (C–V), conductance–voltage (G–V), and current–voltage characteristics of fluorinated amorphous carbon (a-C:Fx) films using metal/a-C:Fx/Si and metal/a-C:Fx/metal structures, respectively. Samples annealed in a vacuum were also studied. The C–V curves of the as-deposited sample are stretched about the voltage axis. Interface state density of 4.1×1011?cm-2?eV-1 at the midgap was calculated. Annealing the sample deposited on Si in a vacuum caused more frequency dispersion in the C–V and G–V curves, probably due to the diffusion of carbon into silicon. The bulk density of states for samples deposited on metal, measured by space-charge-limited current technique, decreased from 4×1018?eV-1?cm-3 for the as-deposited sample, to 7×1017?eV-1?cm-3 for the annealed sample.