Electronics

Transistor Pinouts

Pinouts for common through-hole transistor packages — TO-92, TO-220, TO-247, SOT-23.

Updated Apr 19, 2026 2 min read

Always verify with the datasheet — TO-92 pinouts in particular vary wildly between part numbers.

TO-92 (viewing flat face)

PartPin 1Pin 2Pin 3Notes
2N3904 (NPN)EBCEBC order
2N3906 (PNP)EBCEBC order
2N2222AEBCEBC
2N2907AEBCEBC
BC547 / BC337CBECBE (European ordering!)
BC557 / BC327CBECBE
2N7000 (N-MOSFET)SGDSGD
BS170 (N-MOSFET)SGDSGD
TIP120 (NPN Darlington, TO-220)BCEBCE

TO-220 / TO-247 (leaded tab)

BJT 2N3055 / MJE3055Pin 1 B, Pin 2 C (tab), Pin 3 E
N-MOSFET IRF540 etc.Pin 1 G, Pin 2 D (tab), Pin 3 S
P-MOSFET IRF9540Pin 1 G, Pin 2 D (tab), Pin 3 S
LM317 / LM7805Pin 1 ADJ/IN, Pin 2 OUT (tab), Pin 3 IN/OUT — check each!

SOT-23 (top view, markings visible)

BJT (MMBT3904 etc.)Pin 1 B, Pin 2 E, Pin 3 C
MOSFETPin 1 G, Pin 2 S, Pin 3 D

Notes

  • US transistors often use EBC (2N3904 family). European BC-series often use CBE. Swapping them may appear to work but with catastrophically wrong gain.
  • The metal tab on TO-220/TO-247 is almost always internally connected to the middle pin (drain/collector).
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