We have analyzed the influence of rapid thermal annealing (from 300 to 1050 degrees C) on the optical properties of a-SiNx:H. Three compositions were investigated: x = 0.97, x = 1.43 and x = 1.55. Two different behaviors are observed depending on whether the as-grown nitrogen to silicon ratio of the samples is above or below the percolation threshold (x = 1.1) of Si-Si bonds, in the matrix of silicon nitride. The samples with x: = 1.43 and 1.55 experience an increase of the Tauc coefficient (B) and a decrease of the Urbach parameter (E-0) at low annealing temperatures. while at high temperatures the trend is inverted. On the contrary, the samples with x = 0.97 show a slight and continuous increase of B and a similar decrease of E-0. The different behavior of the films with x < 1.1 is explained by the percolation of the Si-Si bonds, which maintains the order of the structure at high annealing temperatures, preventing the inversion of the trends of B and E-0.