Nickel disilicide (NiSi2) layers were synthesized by nickel ion implantation into silicon substrates using a metal vapor vacuum-arc ion source. The electrical transport properties were studied before and after annealing using sheet resistivity and Hall effect measurements from 30 to 400 K, and the results showed surprising features very different from those generally reported NiSi2 layers. The temperature dependence of sheet resistivity Rs(T) and Hall mobility μH(T) in the as-implanted samples showed peculiar peak and valley features varying from sample to sample, depending on the preparation conditions. However, after annealing, the differences between samples seemed to have diminished in that they all showed similar shapes in both the Rs(T) and the μH(T) curves. A two-band model was proposed to explain the observed electrical transport properties. © 2002 American Institute of Physics.