The correct answer is: A. A semiconductor is a material whose conductivity is same as between that of a conductor and an insulator.
A semiconductor is a material that has electrical conductivity between that of a conductor and an insulator. Semiconductors are used to make a wide variety of electronic devices, including transistors, diodes, and integrated circuits.
Option B is incorrect because the conductivity of a semiconductor is not the average value of the conductivity of a metal and an insulator. The conductivity of a semiconductor can be much higher than the conductivity of an insulator, but it is still much lower than the conductivity of a metal.
Option C is incorrect because a semiconductor does not conduct only half of the applied voltage. The amount of current that flows through a semiconductor depends on the applied voltage, the temperature, and the semiconductor material.
Option D is incorrect because a semiconductor is not made of alternate layers of conducting material and insulator. Semiconductors are made of a single material that has the ability to conduct electricity under certain conditions.