The other day, a friend had asked me about the difference between a BC108 and BC108C, and this got me wondering about part numbers.

The 2N3055, 1N4001, BC108 etc… what do these part numbers actually mean.

Well it turns out that these codes aren’t exactly random and do mean something… sort of…

JOINT ELECTRON DEVICE ENGINEERING COUNCIL (JEDEC) CODE

2N3055

2 – This is the number of package leads, minus 1. (I’ve no idea why -1)
N – Semiconductor registered with JEDEC.
The remaining characters are the device specific device code.

EUROPEAN SEMICONDUCTOR CODE (PRO ELECTRON CODE)

BFY55

The first character is the device material.
A – Germanium
B – Silicon
C – Compound material (gallium arsenide etc)
D – Materials with energy gap band of less than 0.6 eV
R – Radiation detectors, photoconductive cells etc.

The next character is the type of device.
A – Low-power diode, voltage-variable capacitor
B – Varicap
C – Small-signal audio transistor
D – Audio power transistor
E – Tunnel diode
F – Small-signal RF transistor
G – Miscellaneous
L – RF power transistor
P – Photoelectric device
R – Low-power controlled rectifier
S – Low-power switching transistor
T – Breakdown devices (Thyristor, Schottky diode etc)
U – High-power switching transistor
Y – High-power rectifier
Z – Zenner diode

The remaining characters are the device specific device code.

JAPANESE INDUSTRIAL STANDARD (JIS)

2SK102

2 – This is the number of package leads, minus 1
S – Always S when a semiconductor registered with EIAJ

The 3rd character indicates the device type:
K – Polarity and application
A – PNP Transistor, high frequency
B – PNP Transistor, low frequency
C – NPN Transistor, high frequency
D – NPN Transistor, low frequency
E – P-gate thyristor
G – N-gate thyristor
H – N-base unijunction transistor
J – P-channel FET
K – N-channel FET
M – Bi-directional triode thyristor

The remaining characters are the device specific device code.

So, there you have it. For some parts you can tell quite a lot from just looking at the part number before even diving into the internet for a datasheet.

Hope it helps.