Hydrogenated amorphous silicon nitride (a-SiNx:H) films are useful for microelectronic and optoelectronic applications such as passivation layers and antireflection layers. These films are usually deposited by plasma-enhanced chemical vapor deposition (PECVD) using a SiH4/NH3 gas mixture. However, in order to obtain low-hydrogen-content a-SiNx:H films at a low substrate temperature for passivation and/or barrier applications, it is advantageous to use N2 instead of NH3 as the nitrogen source. I obtained transparent a-SiNx:H films with an optical bandgap about 5.0 eV by very high frequency (VHF: 150 MHz)-PECVD using a SiH4/N2 gas mixture in a conventional diode-type reactor at 50 °C. The films were examined with a Fourier transform infrared spectrophotometer (FTIR). The Si-N stretching frequency increases upon increasing VHF power. This shift is induced by the H atom, which is more electronegative than Si, back-bonded to the N atom of the Si-N bonds. Films were stored in an FTIR system containing dry air for 3 months. The changes in local structure in the films during storage deduced from FTIR spectra will be discussed.