Or are they more black metal?
A band-gap is the important concept with semiconductors - energies at which electrons cannot flow. such as copper, are arranged so that outer electrons can easily flow from atom to atom in an electron gas. Insulators have large band-gaps. Electrons are not free flowing - hardly flow at all.
A semi conductor and a conductor differ mostly in the number of free electrons in the element. I'm not clear on what you mean by generate electricity as they do not normally generate electricity but are used to make various electronic components (transistors and such ) silicon,germanium are two examples.
metals have free outer electrons that can move freely and conduct electricity. semi conducters will have this kind of property but they wont have the same structure. sometimes im not sure if this applies, but the electrons in a non metal can spread out over the molecule a bit like the electrons in a metal. this may allow them to conduct.
