Revered members, Conductors have positive temperature coefficient of resistance, that is , their resistance increases with temperature. While for insulators and semi conductors, the resistance decreases with increase in temperature, what we call negative temperature coefficient of resistance. In both semiconductors and conductors, conduction is due to free electrons. The free electrons collide with each other during their motion. Increase of Temperature is a factor for generation of free electrons. But, why resistance increases in conductors while decreases in semiconductors with increase of temperature? After all, in both the cases collisions between free electrons happen.