Stable, electrically conductive, thin film materials are key components for high temperature sensors operating in harsh environments. In this work, nanocomposite Pt-Zr-B and Pt-Si thin film materials were grown to a nominal thickness of 200 nm on both r-cut sapphire (α-Al2O3) substrates using e-beam evaporation, and their structure, morphology, and chemical composition was characterized following thermal treatments in an air laboratory furnace up to 1300°C. In the Pt-Zr-B system, oxidation of a nanolaminate architecture consisting of ZrB2 and pure Pt layers leads to boron oxide evaporation and the formation of Pt grains decorated by tetragonal-ZrO2 nanocrystallites at high temperature. Electrical conductivity measurements with a 4-point probe show that this nanocomposite film structure can maintain a film conductivity > 1x106 S/m up to 1300°C, depending on the Pt/ZrB2 layer thickness ratio. In the Pt-Si system, film compositions were varied to yield either nanocrystalline Pt3Si, Pt2Si, or PtSi phases depending on the Pt-Si ratio, or an amorphous phase at high Si content. Above 1000°C in air, Pt-oxide and Si-oxide phases form and coexist with the Pt-Si phases, and some Pt-Si film conductivities remain as high as 1x106 S/m after annealing at 1000°C for 6 hours. It was found that a 100 nm thick amorphous alumina capping layer grown by atomic layer deposition (ALD) aids in limiting film oxidation, but film stress leads to regions of delamination.