In conductors, as temperature increases, the thermal agitation of lattice ions increases, causing more frequent collisions for the drifting free electrons. This decrease in relaxation time leads to an increase in electrical resistance. In contrast, for semiconductors, an increase in temperature provides sufficient thermal energy to excite more electrons from the valence band across the energy gap into the conduction band. This exponentially increases the number density of charge carriers (electrons and holes), which significantly decreases the electrical resistance.