The electrical characteristics of the low-dielectric-constant SiOC(-H) thin films with Al/SiOC(H)/p-Si(100)/Al metal-insulator-semiconductor (MIS) structures have been investigated by using current-voltage (I-V), capacitance-voltage (C-V), and conductance-voltage (G/w-V) measurements. The SiOC(-H) films were deposited by using plasma enhanced chemical vapor deposition (PECVD) with different radio-frequency (rf) powers. Conductance and capacitance measurements were used to extract the interface state density in the MIS structures. From the experimental data and subsequent quasi-static C-V analysis, the energy distribution of the interface state density was obtained. The interface state density of the as-deposited and 400 °C-annealed MIS structures decreased with increasing rf powers whereas the fixed charge density increased with increasing rf powers. The interface state densities and their electrical properties are strongly influenced by the radio frequency power.