We present an {\it ab initio} analysis of electron conduction through a
C60 molecular device. Charge transfer from the device electrodes to the
molecular region is found to play a crucial role in aligning the lowest
unoccupied molecular orbital (LUMO) of the C60 to the Fermi level of the
electrodes. This alignment induces a substantial device conductance of ∼2.2×(2e2/h). A gate potential can inhibit charge transfer and
introduce a conductance gap near EF, changing the current-voltage
characteristics from metallic to semi-conducting, thereby producing a field
effect molecular current switch