I'm a hobbyist and as such I have an assorted collection of transistors. Most of them, if not all, have a cabalistic string after their names. Case in point is the 2N2222, which displays a "A331" right below its name. Other transistors may have different strings, but most of them show something.

I wonder what those strings mean. Google provided me a few scattered links about this subject, but none was satisfying.

On a separate issue, I find it a bit frustrating that I cannot identify a transistor's maker. There is obviously scarce room on a BJT transistor to print the maker's name, but that would help when one downloads a specific transistor's datasheet from that famous and quite useful AllDataSheet site. Instead of "A331" (or in addition to it thereof) they might have some identification string. Most transistors are made in China today, but they may differ slightly when it comes to their characteristics.

Thanks for any enlightenment on this topic.


1 Answer 1


The usual practice is to put some manufacturer-specific code that identifies which lot the device came from. On parts with more room than a TO-92 or TO-18 provides, you might get a one-digit factory code for which factory the part was made in, combined with a four-digit date code consisting of the last two digits of the year and two digits indicating which week of the year it was made in. But fitting that along with the part number on a TO-92 or TO-18, let alone a SOT-23 or SC-70, is pretty tough, so other codes are used instead.

There is no standard, so without knowing the manufacturer, you're out of luck. Even if you do know the manufacturer, these codes are meant mostly for the manufacturer's internal reference, so they might not be explained on the datasheet. Some manufacturers do, others don't. If they don't, you'd have to contact the manufacturer and ask. If the manufacturer no longer exists, or has gotten bought up by another company decades ago, you're probably just out of luck.

Note that in your specific case, the code you're looking for is probably just "331". The A probably means it's a 2N2222A.

  • \$\begingroup\$ Generally it is an OEM specific date code. This gives them traceability required by some of there customers. \$\endgroup\$
    – Gil
    Oct 6, 2022 at 15:41

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