Transistor means transfer of a signal across a resistor. It is a semiconductor device. It can produce electrical oscillations, amplify small alternating currents and produce rectification. Transistor is an efficient substitute for thermionic valves.
Advantages of transistors over thermionic tubes.
(i) Transistors are very small in size while valves are large in size.
(ii) Transistor do not require heating while valves required to be heated.
(iii) Transistor consumes only small power while valve consumes large power.
(iv) Transistor have long life periods.
(v) The response time of transistors is very small.
(vi) Valves require warming up time.