Final answer:
Lightning arrestors use silicon as the semiconductor material to control electrical surges, safely directing excessive voltages to the ground.
Step-by-step explanation:
The semiconductor blocks in a lightning arrestor are typically made from silicon. Silicon is a widely-used semiconductor material that can act as both a conductor and insulator, depending on the conditions such as the presence of impurities (doping) or electric field. These properties make silicon ideal for controlling electrical surges in lightning arrestors, ensuring that excessive voltages are safely directed to the ground instead of damaging electrical systems.