The factor that determines whether a material is a conductor,  semiconductor or insulator is the amount of free electrons it has. For  example, a silicon lattice has no free electrons because they’re all  bonded to one another. This makes it an insulator. Copper has free  electrons in a pure state, making it a great conductor. Some materials  semi-conduct due to the stacking of P-type and N-type doping. This will  allow current to flow in one direction, but not the other.

I think that silicon chips are the coolest because they allow for  logic gates. Logic gates got me into electrical engineering in the first  place due to their application in digital electronics. A little  background information- just in case you don’t know what logic gates  are:
Logic Gates (a.k.a. Boolean Gates)

• Perform boolean (true/false) functions. 
  • You can think of these as ‘if’ functions. Example, if I1 and I2 are 1, then O is 1. (This is called an AND gate)
• There are several types of logic gates: 
  • AND gates, NAND gates, OR gates, NOR gates, XNOR gates, NOT gates, ect.
• Logic gates are everywhere. You’re using them right now as you read this.

References:

Brain, M. (2021, February 11). How semiconductors work. HowStuffWorks. Retrieved January 26, 2023, from https://electronics.howstuffworks.com/diode.htm

Contributor, T. T. (2020, December 16). What is Logic Gate (and, or, XOR, not, Nand, nor and xnor)? A definition from whatis.com.  WhatIs.com. Retrieved January 26, 2023, from  https://www.techtarget.com/whatis/definition/logic-gate-AND-OR-XOR-NOT-NAND-NOR-and-XNOR