We study electronic transport within a lithographically defined silicon nanowire for zero and finite bias. The 10-nm wide and 500-nm long nanowire is fabricated by advanced electron-beam lithographic techniques. Transport experiments reveal clear quantum size effects in the conduction through the wire. Energy quantization within the wire leads to a shift in conduction threshold. Quantum interference effects cause an oscillatory pattern in the conductance. At low source-drain bias, transport is dominated by shallow tunneling barriers. At higher bias, additional nanowire modes are found to contribute to the conductance.