The influence of rapid thermal annealing treatments on the interface characteristics of Al/SiNx:H/InP devices was analyzed. The insulator was obtained by jan electron cyclotron resonance plasma method at a 200 degrees C-deposition temperature. The films were deposited in a single deposition run but in two steps: first, we deposited the bottom layer with a film composition of x = 1.55 and then the top layer with x = 1.43. Total film thickness was 500 Angstrom in one set of samples and 200 Angstrom in the other one. Annealings were conducted in Ar atmosphere for 30 s in a temperature. range between 400 and 800 degrees C To characterize the electrical behavior of these devices, capacitance-voltage (C-V) and deep level transient spectroscopy; (DLTS) measurements-have been performed on each sample. This last characterization shows the presence of features in the spectra at E-c - 0.2 eV, E-c - 0.25 eV, E-c - 0.38 eV. The last one is due to phosphorus-vacancies, V-P. Devices with 200-Angstrom-thick insulator present the minimum interface trap densities. According to the-DLTS analysis, this minimum (2 x 10(11) cm(-2)eV(-1)) is achieved on the 400 degrees C-annealed samples, A tentative explanation of these results is given in terms: of a possible InP surface passivation due to the fact that nitrogen atoms coming from the insulator can fill phosphorus vacancies, giving rise to a low defective insulator/semiconductor interface, This process is enhanced by rapid thermal, annealing treatments at moderate temperatures (400-500 degrees C).