In order to develop reliable high voltage integrated circuits (HVICs), the characteristics of semi-insulating plasma-deposited amorphous silicon nitride (a-SiN:H) films as resistive field shields, are examined, the reliability of their application to HVICs are studied. The surfaces of these semi-insulating films were unstable, and it was concluded that these films must be covered with a final passivation film such as an insulating plasma-deposited a-SiN:II film. The transverse electrical conduction mechanism of these films is briefly discussed.