Which of the following statement is correct ?

• A. A semi-conductor is a material whose conductivity is same as between that of a conductor and an insulator
• B. A semi-conductor is a material which has conductivity having average value of conductivity of metal and insulator
• C. A semi-conductor is one which conducts only half of the applied voltage
• D. A semi-conductor is a material made of alternate layers of conducting material and insulator