If you know the achanism of working of semiconductors, you will realise that semiconductors conducts electricity only at higher temperatures, as at high temperatures the bonded electrons gains enough energy to move out into the lattice. When temperature is not high, semiconductors do not conduct electricity. So, usage of semiconductors allow us to regulate current in circiut with on and off flexibility. If we use conductors, we cannot have this option as it will always conduct electricity. So it cannot be "switched off". This is why we use only semiconductors but not conductors to conduct current in household circuits.