NPN:

Figure: The symbol of an NPN Bipolar Junction Transistor.

NPN is one of the two sorts of bipolar transistors, where the letters "N" (negative) and "P" (positive) stands for the majority charge carriers in the different regions of the transistor. Several bipolar transistors employed today are NPN, since electron mobility is higher than as compared to the hole mobility in semiconductors, permitting much greater currents and much faster operation.

NPN transistors contain a layer of P-doped semiconductor (the "base") among the two N-doped layers. A small current that is entering the base in common-emitter mode is amplified in the collector output. In other words, an NPN transistor is "on" while the base of it is pulled high relative to the emitter.

The arrow (in figure) in the NPN transistor symbol is on the emitter leg and points in the direction of the conventional current flow while the device is in forward active mode.

One mnemonic device for making out the symbol for the NPN transistor is "not pointing in, or 'not pointing, no' "