The present article reports a study of current–voltage (J–E) and capacitance–voltage (C–V) measurements on metal–insulator–semiconductor diodes, using SiNx:H as an insulator layer and Si or InP as semiconductors. We have deposited SiNx:H films by distributed electron cyclotron resonance plasma enhanced chemical vapor deposition at floating temperature, with physical properties similar to films prepared at 800 °C by low pressure chemical vapor deposition. Silane and nitrogen were used as the reactive gases. The experimental results show that the resistivity (ρ) and the critical field (EC) are a strong function of the dielectric composition. For films deposited under optimum conditions, ρ was equal to 1016 Ω cm and EC reached 3.65 or 4.5 MV/cm for Al/SiNx:H/Si and Al/SiNx:H/InP diodes, respectively. The dominant mode of electronic conduction appears to be the Poole–Frenkel emission. The postmetallization annealing (PMA) has no significant effect on these bulk properties (ρ, EC and electronic conduction). On the contrary, PMA has been shown to mainly affect the properties of both SiNx:H/Si and SiNx:H/InP interfaces. The optimized Al/SiNx:H/Si fabrication procedure induced a midgap interface state density (Dit) of 6×1- - 010 eV-1 cm-2 evaluated by high frequency and quasistatic C–V characteristics. In the case of Al/SiNx:H/InP diodes, we have found that the carrier trapping by direct tunneling near the SiNx:H/InP interface is dominant. © 1997 American Vacuum Society.