On the basis of conductivity: On the basis of the relative values of electrical conductivity (σ) or resistivity (ρ = 1/σ), the solids are broadly classified as:
They possess very low resistivity (or high conductivity).
They have resistivity or conductivity intermediate to metals and insulators.
They have high resistivity (or low conductivity).
The values of ρ and σ have given above are indicative of the magnitude and could well go outside the ranges as well. Relative values of the resistivity are not the only criteria for distinguishing metals, insulators and semiconductors from each other.