SMD transistors and diodes rarely have full part numbers printed on their packages. Instead, they use short 2- to 3-character SMD codes. This guide explains how to read them and provides the most common SOT-23, SOT-323, SOT-563 and DFN transistor marking codes, as well as Schottky, switching and Zener diode codes.
SMD packages are too small for full numbers like “BC817-40” or “1N4148”. Manufacturers use short package laser marks that map to full part numbers.
The problem: the same code can map to different parts from different vendors. You must decode using:
Below is a collection of the most seen markings on real production PCBs.
| Code | Full Part Number | Type |
|---|---|---|
| 1AM | MMBT3904 | NPN general-purpose |
| 1AW | MMBT3906 | PNP general-purpose |
| A1S | BC817 | NPN general amplifier / switch |
| 1F | 2N7002 | N-channel MOSFET (logic-level) |
| 2F | BSS138 | N-channel MOSFET |
| 3F | BSH103 | N-FET, low Rds |
| 2A | BC847 | NPN low noise |
| 2B | BC857 | PNP low noise |
Smaller RF/digital packages often use two-character marks.
| Mark | Device | Use |
|---|---|---|
| K6 | BC849 | NPN |
| K8 | BC859 | PNP |
| A7 | 2N7002DW | Dual MOSFET |
| 6A | SSM3K15 | N-MOSFET (Toshiba) |
Diodes usually use 1–2 letter marks.
| Mark | Part | Type |
|---|---|---|
| A7 | BAT54 | Schottky |
| LK | 1N4148WS | Fast switching diode |
| SS | SS14 | Schottky, 1A |
| T4 | BAV99 | Dual switching diode |
| Z2 | BZX84-C5V1 | Zener 5.1V |
| Z5 | BZX84-C12 | Zener 12V |
Packages like SOT-363, SOT-563 often contain matched transistor pairs.
| Mark | Device | Description |
|---|---|---|
| 6A | BCM847BS | Dual NPN |
| 6B | BCM857BS | Dual PNP |
| A6 | 2N7002DW | Dual MOSFET |
This cheat sheet covers the most common SMD transistor codes and SMD diode codes used in modern consumer, industrial and power electronics.
