Numbering Systems in Semi conductor devices

    

1) Every Semi conductor device numbered by five alfa-numeric symbols.
     Exa. BF194
              BFX63.
     Generally Devices with two letters and three digits are intended for entertainment and consumer  equipments (Ex. BF194)
     Devices with three letters and two digits are used for industrial or professional equipments. (Ex. BFX63)

2) First letter of symbol indicate nature of semiconductor material.
     
      A for Germanium
      B for silicon
      C for Gallium arsanide.
      R for compound semiconductor material

Exa. AC125 is germanium transistor
        BC149 is silicon transistor

3) second letter identifies the device and its function in the circuit.

     A - Diode.
     B - Varactor diode (variable capacitor diode).
     C - audio frequency (AF) Low power transistor.
     D - AF Power transistor.
     E - Tunnel Diode.
     F - High frequency (HF) Low power transistor.
    G - Miscellaneous device.
    H - Device sensitive to Magnetic.
    K - Hall-effect device.
    L - High frequency(HF) power transistor.
    M - Hall-effect modulator.
    N - Photocoupler
    P - Radiation sensitive diode(Light detector).
    Q - Radiation generating diode (Light emitter).
    R - Thyristor (SCR or Triac or other power switching device)
    S - Low power switching Transistor
    T - High power transistor.
    U - Power switching Transistor.
    W - surface acoustic wave device
    X - Diode, Multiplier.
    Y - Power device(rectifying).
    Z - Zener Diode(voltage reference)

Other numbering system also exist
for Exa. 1N4001 is silicon diode. 2N3903 is silicon NPN general purpose transistor.

Here,

FIRST NUMBER                                SECOND LETTER                       SUBSEQUENT NUMBER

    1.   = Diode                                      N                                                       Serial number of device
    2.  = Transistor
    3.  = FET