  Current thermometry techniques lack the spatial resolution required to see
the temperature gradients in typical, highly-scaled modern transistors. As a
step toward addressing this problem, we have measured the temperature
dependence of the volume plasmon energy in silicon nanoparticles from room
temperature to 1250$^\circ$C, using a chip-style heating sample holder in a
scanning transmission electron microscope (STEM) equipped with electron energy
loss spectroscopy (EELS). The plasmon energy changes as expected for an
electron gas subject to the thermal expansion of silicon. Reversing this
reasoning, we find that measurements of the plasmon energy provide an
independent measure of the nanoparticle temperature consistent with that of the
heater chip's macroscopic heater/thermometer to within the 5\% accuracy of the
chip thermometer's calibration. Thus silicon has the potential to provide its
own, high-spatial-resolution thermometric readout signal via measurements of
its volume plasmon energy. Furthermore, nanoparticles in general can serve as
convenient nanothermometers for \emph{in situ} electron microscopy experiments.
