Hydrogenated amorphous silicon nitride (a‐SiNxH) films have been deposited on InP substrates by the low‐temperature (185 °C) plasma enhanced chemical vapor deposition technique in order to realize metal‐insulator‐semiconductor capacitors. It has been found that the electronic properties of the InP‐insulator interface are greatly improved if the insulator deposition is carried out in the presence of AsH3during the first stage of the process (interface state density in the range of a few 1011eV−1 cm−2in the upper part of the gap). The deposited films exhibit very high resistivity (1017&OHgr; cm) and high breakdown voltage (3×106V/cm). In similar conditions, no beneficial effect of PH3during the deposition has been noticed.