The temperature-dependent resistivity measurements of Ni-Si silicide films with 18-290 nm thicknesses are studied as a function of temperature and film thickness over the temperature range of 100-900K. The most striking behavior is that the variation of the resistivity of the films with temperature exhibits an unusual behavior. The total resistivity of the Ni-Si silicide films in this work increases linearly with temperature up to a T-m temperature, thereafter decreases rapidly and finally reaches zero. Our analyses have shown that in the temperature range of 100 to T-m (K), parallel-resistor formula reduces to Matthiessen's rule and theta(D) Debye temperature becomes independent of the temperature for the given thickness range, whereas at high temperatures (above T-m) it increases slightly with thickness. theta(D) Debye temperature have been found to be about 400-430 K for the films.