What About the Bonding of Silicon Makes It Useful as a Semiconductor

What about the bonding of silicon makes it useful as a semiconductor but not as a conductor of electricity?

A) The electrons are transferred forming ions that conduct electricity.
B) The electrons are shared in covalent bonds between atoms.
C) The electrons form a "sea of electrons" that move between many atoms.
D) The electrons are somewhat shared and somewhat transferred because it is a metalloiD.