A semiconductor is a material that lies between the conductors and insulators of the electrical world. It has a unique ability to modify its electrical properties depending on environmental changes such as temperature, electric field or light intensity. In this way, semiconductors can be used in a range of applications, such as transistors, logic circuits, LEDs.

The theoretical basis of semiconductors lies in their band structure. All materials have an energy band structure, which divides the material into different energy states and characterizes the way that electrons interact with it. For semiconductors, there is an energy gap between the valence and conduction band, which allow electrons to transition from their occupied to unoccupied energy states, thus allowing the flow of electric current. This process can be altered by external influences such as an electric field, temperature, or intensity of light.

As such, semiconductors have been fundamental components of our modern electronics. Transistors are used to amplify or switch electronic signals, logic circuits allow for computing power, and LEDs are used to create light. All of these devices use semiconductors in different ways to manipulate the electrons and their energy states to accomplish the desired effect.

In conclusion, semiconductors are one of the most important materials used by the electronics industry today. Their unique energy band structure allows them to manipulate the movement of electrons and thus affect the electrical properties of materials. With advances in semiconductor technology, the applications of semiconductors continue to expand, allowing for ever more intricate and powerful circuits and devices.