The resistance of pure metals increases as the temperature rises. The explanation for this is that the number of electrons in the conduction band increases, reducing mobility and thereby increasing resistance. With the increase in temperature, the thermal motion among the atoms of the lattice also increases due to which the charge carriers bump more into the lattice vibrations which increases the resistivity of the pure metal. In the case of semiconductors, this theory is not true, and therefore, there are semimetals also in which the two effects compete with each other, and trends in temperature range can be observed.