The reaction of scandium films with their (100) silicon substrates leads to the formation of two different silicides. In a temperature range from 500 to 600°C one observes the formation of the orthorhombic ScSi. The modalities of this reaction imply that it is diffusion-controlled, although that has not been explicitly verified. Above 900°C one observes within a narrow range of temperatures the formation of hexagonal ScSi1.7, which is clearly controlled by nucleation. The room-temperature resistivity of ScSi was measured at 21 μω· cm. Comparison with the resistivity at liquid helium temperature, 1.5 μω· cm provides a measure of the minimal room-temperature resistivity. The mechanical weakness of the ScSi1.7 made it difficult to obtain reliable values for the resistivity of that compound; room temperature values of about 38 μω· cm were obtained. (The resistivity values reported here correspond to polycrystalline films with various degrees of random orientation. Of necessity they were derived without taking into account the effects of crystalline anisotropy.) A systematic analysis of the results obtained with scandium throws a welcomed light on the still poorly understood modes of formation of TiSi2 and of the silicon-rich rare-earth compounds. © 1991.