What is a semi-conductor?

A semiconductor is a material, typically a solid element like silicon or germanium, that has electrical conductivity between a conductor (like Aluminium, Al resistivity of ρ = 10^-8Ωm) and an insulator (like glass, SiO₂ resistivity ρ = 10¹⁴Ωm).

Resistance (R) is \(R = \rho\frac{l}{A}\).