Introduction:

We know that the Transistor is a Semiconductor Device that can be either used as a Switch or an Amplifier. The Transistor can be classified as:

1. Bipolar Junction Transistor (BJT) and 

2. Field Effect Transistor (FET)

This classification is based on the number of charge carriers contributing to the conduction of the device. As the name indicates in the Bipolar Junction Transistor (BJT) both the charge carriers electrons and holes contribute to the conduction of the device. Whereas in the Field Effect Transistor (FET) the conduction is either due to electrons or holes. As such these devices are also called Unipolar Devices. 

These Transistors can further be subclassified as follows:

1. A BJT can be of two types 

   1. N-P-N Transistor 

   2.  P-N-P Transistor

2. A FET can be of two types

   1. Junction Field Effect Transistor (JFET) and 

   2. Metal Oxide Semiconductor FET (MOSFET)

3. A JFET can be of two types:

   1. N-Channel FET amd 

   2. P- Channel FET 

4. A MOSFET can be of two types

   1. N- Channel MOSFET

   2. P- Channel MOSFET

5. An N-Channel MOSFET can be of two types:

   1. Enhancement Type MOSFET and

   2. Depletion Type MOSFET

Figure 1 shows the classification of the Transistors.