This work aims to apply modern spherical indentation methods to micromechanical testing at exceptionally high temperatures. Tests were performed on a polycrystalline silicon thin film. This film was deposited on a (100) monocrystalline silicon substrate with an intermediate Oxide layer, mimicking the structure of a silicon-gate technology field effect transistor. The indentation tests were conducted at 500 °C and 700 °C. The obtained flow curves are discussed regarding the microscopically observed deformation behavior and compared to literature data concerning the high-temperature plasticity of silicon. The results suggest kink-pair controlled, thermally activated glide of dislocations as the dominating plastic deformation mechanism for both investigated temperatures.