  We have simultaneously measured conductance and thermoelectric power (TEP) of
individual silicon and germanium/silicon core/shell nanowires in the field
effect transistor device configuration. As the applied gate voltage changes,
the TEP shows distinctly different behaviors while the electrical conductance
exhibits the turn-off, subthreshold, and saturation regimes respectively. At
room temperature, peak TEP value of $\sim 300 \mu$V/K is observed in the
subthreshold regime of the Si devices. The temperature dependence of the
saturated TEP values are used to estimate the carrier doping of Si nanowires.
