The phase growth sequence, structural, electrical and optical properties and thermal stability of platinum silicide films were investigated as a function of silicide film thickness in the range 133-2506 Angstrom. The platinum silicide films were formed by ex situ silicidation of Pt films sputter-deposited onto n(-)-Si (100) substrates. Films of all thicknesses were polycrystalline brit exhibited columnar growth morphology and strong orientation effects. The orientation, grain size, electrical resistivity, specular reflectance and thermal stability were observed to be strongly thickness dependent. The temperature at which the film properties degraded increased with film thickness. The degradation mechanism appeared to be Pt diffusion into Si accompanied by the disintegration of the PtSi layer and the formation of an additional Pt3Si phase.