In this article we analyze the effect of the in situ thermal treatments on the properties of the Ir/n-type Si (111) Schottky contacts. The samples were annealed in the evaporation system at 400 degrees C for 15 min and at 450 degrees C for 15 min or 2 h. Rutherford backscattering spectroscopy spectra and secondary ion mass spectroscopy compositional profiles indicate that as result of the different thermal treatments performed in the samples there is a clear diffusion of silicon into the iridium layer but the composition of the metal-semiconductor interface cannot be determined. It has been shown previously that a small quantity of IrSi can be formed at an Ir-Si interface when Ir layers are deposited on Si. The current-voltage-temperature (I-V-T) behavior of these diodes indicates that it is dominated by the effect of spatial fluctuations of the surface barrier. After the thermal treatment at 400 degrees C for 15 min the diodes show I-V characteristics that can be perfectly justified by the unidimensional model of the thermionic emission theory. The Schottky barrier value at 0 K (0.92 eV) and the temperature coefficient of the barrier (3.10(-4) V/K) corresponds with that previously reported for the IrSi. When the annealing temperature is raised to 450 degrees C, the resulting devices show a nonhomogeneous barrier with similar values to those found at room temperature. Increasing the annealing time to 2 h leads to devices showing an increase in the ideality factor value (1.12), along with a barrier height value at room temperature (0.86 eV) which coincides with that previously reported for the IrSi1.75. The 0 K barrier height (0.72 eV) indicates that a phase transformation at the interface has taken place.