Welcome to circuitspedia.com

how to read diode markings

Semiconductor device numbering system

Transistor identification guide

 How to identify a diode and its specification

Each Semiconductor devices have a special numbering coding as per the specification of those components. All Components have a particular symbolic numbering with Alphanumeric coding for represents their characteristics of the material and other parameters. There is an international numbering system for all semiconductor devices and components.

  • The 1st letter of the symbol indicates the nature of semiconductor Material. A for germanium, B for Silicon, C for gallium arsenide and R for compound (eg- cadmium sulphate). If any transistor number is AC125 then it is a germanium transistor and if BC148 is a silicon transistor.
  • The 2nd Letter of any symbol indicates the device type and its function in the circuit eg  C means small signal and D means power.
  • Commonly two Letters and three Numbers and three letters and two numbers are used. Two Letters and Three numbers (eg BF 194) are used for Consumer equipment or for Entertainment purposes. Whereas the devices three letters and two numbers ( eg BFX 63 ) components are used for industrial or professional.

First letter = Semiconductor material

A – Germanium
B – Silicon
C – Gallium Arsenide
D – Photodiodes


Second Letter = Application

A – General Purpose diode

B – Variable capacitance (Varactor) diode

C – Audio Frequency (AF) Low Power Transistor

D – AF Power Transistor

E – Tunnel diode

F – High frequency(HF) Low power transistor

G – Multiple Devices

H – Magnetic Sensitive devices

K – Hall effect Modulator

P – Photodiode/Radiation sensitive diode

Q – Light Emitting Diode/Radiation generating diode

R – Thyristor (SCR or Triac)

S – Low Power Switching transistor

T – High Power transistor

U – Power Switching transistor

X – Diode, Multiplier

Y – Power rectifier

Z – Zener Diode


Third letter –

 The third letter does not have any particular significance. The letter is used to mention the specialized application of the diode.

The second letter is ‘N’, and then the first digit is 1 for diodes, 2 for transistors, 3 for four-leaded devices, and so forth. But 4N and 5N are only used for optocouplers. The sequential numbers run from 100 to 9999 and indicate the approximate time the device was first made. various things. For example, a 2N2222A is an enhanced version of a 2N2222. It has higher gain, frequency, and voltage ratings. Always check the datasheet.

Examples: 1N4007, 1N914 (diode) and 2N2222, 2N3904 (transistors).

Japanese Industrial Standard (JIS)

 These part numbers take the form: digit, two letters, sequential number, [optional suffix] Digits are 1 for diodes, 2 for transistors, and so forth. The letters indicate the type and intended application of the device according to the following code.


SA – PNP HF (High Frequency) Transistor

SB – PNP AF(Audio frequency) Transistor

SC – NPN HF(High Frequency ) Transistor

SD – NPN AF Transistor

SE – Diodes

SF – Thyristors

SG – P-channel  FET


SK – N- channel FET

SM – Triac


SR – Rectifier

SS – Signal diode

ST – Avalanche diode

SV – Varicap

SZ – Zener diode


If any suffix presents then for this suffix Always check the datasheet because it represents various things.  For example, a 2N2222A is an enhanced version of a 2N2222. It has higher gain, frequency, and voltage ratings.

an additional letter for Zener Diodes will appear after the numbers. This letter denotes the tolerance of the Zener voltages. The following letters are used for denoting of tolerance of Zener Diodes.
A ±1%
B ±2%
C ±5%
D ±10%

Zener diodes have additional characters which will indicate the zener voltage.
Ex: 5V1 indicate 5.1V

Instead of 2N and so forth, some manufacturers use their own system of designations. Some common prefixes are:

MJ: Motorola power, metal case

MJE: Motorola power, plastic case

 MPS: Motorola low power, plastic case

MRF: Motorola HF, VHF and microwave transistor

RCA: RCA device

TIP: Texas Instruments (TI) power transistor, plastic case

TIPL: TI planar power transistor TIS: TI small signal transistor (plastic case)

 ZT: Ferranti

ZTX: Ferranti

 Examples: ZTX302, TIP31A, MJE3055.

About the Author


Hi, My name is Aman Bharti, I am interested in making and study of Electronics & circuit diagram. I like to share the knowledge and all ideas with people which I get from My Experiment & from different sources. I try to provide any circuit details deeply with test results as possible. If you want to give a suggestion or comments on anything, please leave your comment in the comment box of the related page.

Leave a Reply

Your email address will not be published. Required fields are marked *