Interdiffusion of a few nanometers thick C layer with Mo and Si under annealing at a temperature of 600 °C was studied using X-ray photoelectron spectroscopy sputter depth profiling. A strong diffusion asymmetry of C in a Mo–Si layered structure is observed. C does interdiffuse with Mo, however, even at 600 °C, no interdiffusion of Si and C was observed. Based on these results, the thermal stability of Mo/Si-based layer structures was improved by depositing a Si/C/Mo2C/C/Si layer structure. This structure shows superior thermal stability at 600 °C compared to the Mo2C/Si and Mo/Si layer structure.