  We report a transport study of exfoliated few monolayer crystals of
topological insulator Bi$_2$Se$_3$ in an electric field effect (EFE) geometry.
By doping the bulk crystals with Ca, we are able to fabricate devices with
sufficiently low bulk carrier density to change the sign of the Hall density
with the gate voltage $V_g$. We find that the temperature $T$ and magnetic
field dependent transport properties in the vicinity of this $V_g$ can be
explained by a bulk channel with activation gap of approximately 50 meV and a
relatively high mobility metallic channel that dominates at low $T$. The
conductance (approximately 2 $\times$ 7$e^2/h$), weak anti-localization, and
metallic resistance-temperature profile of the latter lead us to identify it
with the protected surface state. The relative smallness of the observed gap
implies limitations for EFE topological insulator devices at room temperature.
