We have been using so many semiconductor devices and most of the times don’t know what there serial numbers really mean.  Mainly there are 2 numbering standards used;

1. European based Pro-Electron System (for eg 1N4001, 2N2222)
2. American based JEDEC System (BC546, BC547)

1.European based Pro-Electron System

This system uses the following format for numbering the devices ;

XY,[Y],ZZZZ,[S]

X determines the material of semiconductor;

A is Germanium
B is Silicon
C is Gallium Arsenide
R is Compound Materials

Y determines the type of device;

A is Diode, Low power or signal
B is Diode, Variable capacitance
C is Transistor, Audio frequency low power
D is Transistor, Audio frequency high power
E is Diode, Tunnel
F is Transistor, High frequency low power
G is Miscellaneous devices
H is Diode, Sensitive to magnetism
K is Hall effect device
L is Transistor, High frequency power
N is Photocoupler
P is Light detector
Q is Light emitter
R is Switching device, Low power e.g. thyristor, diac, unijunction etc
S is Transistor, Low power switching
T is Switching device power, e.g. Thyristor, Triac.
U is Transistor, Switching power
W is Surface acoustic wave device
X is Diode, multiplier, e.g. varactor
Y is Diode, rectifying
Z is Diode, voltage reference

Y if present determines whether the device in intended for industrial or commercial use.

ZZZZ is the serial number for the device. It goes from 100 to 9999.

S if present determines the gain group of the device;

A is Low gain
B is Medium gain
C is High gain
Not present means any gain

Example

BC546 now shows that it is a Silicon, Transistor with Low Power Audio Frequency.

2. American based JEDEC System

This system used the following format;

X,Y,ZZZZ,[S]

X is a digit which determines the number of PN junctions used in device ;

1 is  Diode
2 is  Bipolar transistors or Field Effect Transistors
3 is Double Gate MOSFETS, SCR’s
4 is  Opto Couplers

Y always remain N

ZZZZ is the serial number of deivce from 100 to 9999

[S] is same as in Pro-Electron System.

Example

1N4001 shows that it is a Diode becuase of only 1 PN juntcion.
2N2222 is a Transistor becuase of 2 in PN junctions.