Circuit Symbols
Drawing style

Transistor symbol

In a bipolar (BJT) symbol the arrow is always on the emitter (E): pointing out means NPN, in means PNP. The base (B) meets the flat bar; the other lead is the collector (C). The MOSFETs drawn here carry their arrow on the body instead.⁠Source 1Source 2Source 3Source 4

Reference Designator Q⁠Source 5

On this sheet

Symbol and what it is doing

no drive
driven

US style

no drive
driven

IEC style

Fig. 1 — NPN transistor, base drive none: C–⁠E open NPN transistor, base drive enough to saturate: C–⁠E conducts
BCEno drive
Fig. 1a — NPN transistor, base drive none: C–⁠E open
BCEdriven
Fig. 1b — NPN transistor, base drive enough to saturate: C–⁠E conducts
BCEno drive
Fig. 1a — NPN transistor, base drive none: C–⁠E open
BCEdriven
Fig. 1b — NPN transistor, base drive enough to saturate: C–⁠E conducts

Turn the base drive on and off. The printed transistor stays the same; the highlight shows when the switch model treats the collector–emitter path as conducting.

Base drive

C–⁠E open. Under the BJT switch model, no base drive gives cutoff: the collector–emitter path is treated as open.

C–⁠E conducts. Under the BJT switch model, sufficient base drive for the connected load gives saturation: the collector–emitter path conducts.

Terminals

B
The base is the terminal drawn against the flat bar; a small base current controls the device.⁠Source 1Source 2
C
The collector is the branch connected to the base bar that has no emitter arrow. The base has its own separate lead to that bar.⁠Source 2
E
The arrow is always on the emitter. It points out of the transistor for NPN and into it for PNP, whichever way the symbol is rotated.⁠Source 1Source 2

Parts of the drawing

  • NPN transistor symbol in US style, with numbered leaders to the emitter arrow, the flat bar and the enclosing circle
1 Flat bar
As in the terminal key.
2 Enclosing circle
The enclosing circle may be omitted from a transistor symbol. With the same internal marks and terminal connections, either drawing represents the same transistor.⁠Source 6
3 Emitter arrow
The emitter arrow points the way conventional current flows through the emitter when the transistor conducts: out of an NPN transistor and into a PNP. Base and collector currents combine to match the arrow's direction.⁠Source 4Source 7Source 8
  • NPN transistor symbol in IEC style, with numbered leaders to the emitter arrow and the flat bar
1 Flat bar
As in the terminal key.
2 Emitter arrow
The emitter arrow points the way conventional current flows through the emitter when the transistor conducts: out of an NPN transistor and into a PNP. Base and collector currents combine to match the arrow's direction.⁠Source 4Source 7Source 8
Fig. 2 — NPN transistor symbol, US style, its marks numberedNPN transistor symbol, IEC style, its marks numbered
  • NPN transistor symbol, US style, turned 0°, with its terminal names attached

    0°

  • NPN transistor symbol, US style, turned 90°, with its terminal names attached

    90°

  • NPN transistor symbol, US style, turned 180°, with its terminal names attached

    180°

  • NPN transistor symbol, US style, turned 270°, with its terminal names attached

    270°

  • NPN transistor symbol, US style, mirrored, with its terminal names attached

    Mirrored

Rotating or mirroring a whole symbol, with its terminal identities and connections preserved, does not change the component. The terminal labels move with the drawing.⁠Source 9

  • NPN transistor symbol, IEC style, turned 0°, with its terminal names attached

    0°

  • NPN transistor symbol, IEC style, turned 90°, with its terminal names attached

    90°

  • NPN transistor symbol, IEC style, turned 180°, with its terminal names attached

    180°

  • NPN transistor symbol, IEC style, turned 270°, with its terminal names attached

    270°

  • NPN transistor symbol, IEC style, mirrored, with its terminal names attached

    Mirrored

Rotating or mirroring a whole symbol, with its terminal identities and connections preserved, does not change the component. The terminal labels move with the drawing.⁠Source 9

Fig. 3 — NPN transistor symbol, US style at 0°, 90°, 180° and 270°, and mirroredNPN transistor symbol, IEC style at 0°, 90°, 180° and 270°, and mirrored

Variants

  • BCE
    BCE

    PNP transistor

    As in the terminal key (E).

  • GDS
    GDS

    N-channel MOSFET

    A MOSFET uses gate voltage relative to source to control its channel between drain and source. The three-terminal form shown here connects its body internally to source.⁠Source 3

    G
    The gate is the insulated terminal drawn parallel to the channel with a gap between them.⁠Source 3
    D
    The drain (D) is the other channel terminal: the channel runs between drain and source.⁠Source 3
    S
    The source (S) is the channel terminal joined to the body in the three-terminal form shown here, so the controlling gate voltage is applied between gate and source.⁠Source 3
  • GDS
    GDS

    P-channel MOSFET

    In the body-arrow MOSFET convention used here, the arrow points toward the channel for N-channel and away for P-channel. Other MOSFET symbol forms place the arrow differently.⁠Source 2Source 3

Telling them apart

  • A MOSFET's gate is drawn beside the channel with a gap between them, and its arrow sits on the body. A bipolar transistor's base lead meets its bar directly, and its arrow sits on the angled emitter lead.⁠Source 2Source 3Source 4
  • In a PNP transistor symbol the emitter arrow points in, toward the base; that inward arrow is the only mark that tells it from an NPN symbol.⁠Source 4Source 8
  • The N in a device's name does not fix which way its arrow points. Each junction arrow points toward the N-type side: an NPN transistor's emitter arrow points out, but an N-channel MOSFET's body arrow points in, toward the channel.⁠Source 2Source 3Source 4
  • In a P-channel MOSFET symbol the body arrow points out, away from the channel, because the arrow points toward the N-type body.⁠Source 2Source 3

Which way the arrow points

  • Diode symbol, US style, its arrow ringed: it points from anode to cathode

    Diode

    Points from anode to cathode

  • NPN transistor symbol, US style, its arrow ringed: it points out of an NPN transistor

    NPN transistor

    Points out of an NPN transistor

  • PNP transistor symbol, US style, its arrow ringed: it points in, toward the base

    PNP transistor

    Points in, toward the base

  • N-channel MOSFET symbol, US style, its arrow ringed: it points in, toward the channel

    N-channel MOSFET

    Points in, toward the channel

  • P-channel MOSFET symbol, US style, its arrow ringed: it points out, away from the channel

    P-channel MOSFET

    Points out, away from the channel

  • Diode symbol, IEC style, its arrow ringed: it points from anode to cathode

    Diode

    Points from anode to cathode

  • NPN transistor symbol, IEC style, its arrow ringed: it points out of an NPN transistor

    NPN transistor

    Points out of an NPN transistor

  • PNP transistor symbol, IEC style, its arrow ringed: it points in, toward the base

    PNP transistor

    Points in, toward the base

  • N-channel MOSFET symbol, IEC style, its arrow ringed: it points in, toward the channel

    N-channel MOSFET

    Points in, toward the channel

  • P-channel MOSFET symbol, IEC style, its arrow ringed: it points out, away from the channel

    P-channel MOSFET

    Points out, away from the channel

Fig. 4 — The arrow on each semiconductor symbol, ringed, with which way it pointsThe arrow on each semiconductor symbol, ringed, with which way it points ⁠Source 2Source 3Source 4Source 7Source 8Source 10Source 11Source 12

Notes

A bipolar transistor is steered at its base

A bipolar transistor has base, collector and emitter terminals. In the current-controlled model used here, base drive controls conduction between collector and emitter.⁠Source 1 Its emitter arrow is read the same way as the triangle in a diode symbol, in the direction of conventional current.

B, C and E name roles, not pin positions

A schematic symbol shows how terminals connect, not where they are on a real part. Terminal letters such as E, B and C or A and K do not give lead order or package layout; the part's own documentation does.⁠Source 9Source 13Source 14 The letters name what each terminal does: base drive controls the path between collector and emitter, and a MOSFET’s gate controls the channel between drain and source.

Check your reading

More questions on the practice page

Pick an answer to see the reason.

  1. Question 1

    This transistor has been turned and its labels hidden. Which lead is its emitter?

    A short horizontal bar with a lead rising straight up from its middle. Two angled leads run down from the bar, one to each side, and bend out sideways; the left-hand one carries an arrow pointing away from the bar. A circle surrounds the drawing.

    A short horizontal bar with a lead rising straight up from its middle. Two angled leads run down from the bar, one to each side, and bend out sideways; the left-hand one carries an arrow pointing away from the bar.

    Not this one Right Answer

    The answer is “The lead on the left”. The base is the terminal drawn against the flat bar; a small base current controls the device.The collector is the branch connected to the base bar that has no emitter arrow. The base has its own separate lead to that bar. The arrow is always on the emitter. It points out of the transistor for NPN and into it for PNP, whichever way the symbol is rotated.

  2. Question 2

    Which transistor is this?

    A short vertical bar with a lead coming in from the right. Two angled leads leave the bar on the left and bend away, one up and one down, and the upper one carries an arrow pointing toward the bar. A circle surrounds the drawing.

    A short vertical bar with a lead coming in from the right. Two angled leads leave the bar on the left and bend away, one up and one down, and the upper one carries an arrow pointing toward the bar.

    Not this one Right Answer

    The answer is “A PNP bipolar transistor”. The arrow is always on the emitter. It points out of the transistor for NPN and into it for PNP, whichever way the symbol is rotated.A MOSFET's gate is drawn beside the channel with a gap between them, and its arrow sits on the body. A bipolar transistor's base lead meets its bar directly, and its arrow sits on the angled emitter lead. In a PNP transistor symbol the emitter arrow points in, toward the base; that inward arrow is the only mark that tells it from an NPN symbol.

  3. Question 3

    This transistor is drawn inside a circle. What would the drawing mean without it?

    BCE

    A circle round a short vertical bar. A lead from the left, labelled B, meets the bar; two angled leads leave it, one up to a lead labelled C and one down to a lead labelled E, and the lower one carries an arrow pointing away from the bar.

    Not this one Right Answer

    The answer is “The same transistor: the circle is optional”. In a PNP transistor symbol the emitter arrow points in, toward the base; that inward arrow is the only mark that tells it from an NPN symbol.A MOSFET's gate is drawn beside the channel with a gap between them, and its arrow sits on the body. A bipolar transistor's base lead meets its bar directly, and its arrow sits on the angled emitter lead. The enclosing circle may be omitted from a transistor symbol. With the same internal marks and terminal connections, either drawing represents the same transistor.

  4. Question 4

    The base is driven, as marked. Under the switch model, what is the collector–emitter path doing?

    BCEdriven

    A lead from the left, labelled B and marked driven, meets a short vertical bar; two angled leads leave the bar, one up to a lead labelled C and one down to a lead labelled E, and the lower one carries an arrow pointing away from the bar. A circle surrounds the drawing.

    BCEdriven

    A lead from the left, labelled B and marked driven, meets a short vertical bar; two angled leads leave the bar, one up to a lead labelled C and one down to a lead labelled E, and the lower one carries an arrow pointing away from the bar.

    Not this one Right Answer

    The answer is “Conducting: the transistor is on”. The emitter arrow points the way conventional current flows through the emitter when the transistor conducts: out of an NPN transistor and into a PNP. Base and collector currents combine to match the arrow's direction.Under the BJT switch model, suitable circuit bias and sufficient base drive put the transistor in saturation; no base drive gives cutoff. The cases omit leakage, transition time and the active amplification region. Under the BJT switch model, sufficient base drive for the connected load gives saturation: the collector–emitter path conducts.

  5. Question 5

    This MOSFET is drawn turned round, with its labels hidden. Which lead is its gate?

    A vertical line with a lead coming in from the right. To its left, across a small gap, is a broken vertical line of three short dashes. Three horizontal lines run left from the dashes: the top and bottom ones turn to leave as leads going up and down, and the middle one, which carries an arrow pointing toward the dashes, joins the upper lead. A circle surrounds the drawing.

    A vertical line with a lead coming in from the right. To its left, across a small gap, is a broken vertical line of three short dashes. Three horizontal lines run left from the dashes: the top and bottom ones turn to leave as leads going up and down, and the middle one, which carries an arrow pointing toward the dashes, joins the upper lead.

    Not this one Right Answer

    The answer is “The lead on the right”. The source (S) is the channel terminal joined to the body in the three-terminal form shown here, so the controlling gate voltage is applied between gate and source.The drain (D) is the other channel terminal: the channel runs between drain and source. The gate is the insulated terminal drawn parallel to the channel with a gap between them.

Answer key

  1. 1

    The lead on the left

  2. 2

    A PNP bipolar transistor

  3. 3

    The same transistor: the circle is optional

  4. 4

    Conducting: the transistor is on

    BCEdriven
    BCEdriven
  5. 5

    The lead on the right

Questions

How do I tell NPN from PNP?
Look only at the emitter arrow. Pointing away from the base means NPN; pointing in toward the base means PNP. Nothing else in the drawing tells them apart.⁠Source 1Source 2Source 4Source 8
Does the circle around a transistor symbol matter?
No. Some drawings leave the circle out. With the same marks and connections inside, the drawing stands for the same transistor either way.⁠Source 6
Why does an N-channel MOSFET arrow point the other way?
Each arrow points toward N-type material, not toward the letter in the name. So the NPN emitter arrow points out, while the N-channel MOSFET's body arrow points in, toward the channel.⁠Source 2Source 3Source 4

Print and files

Printable symbol sheetPrintable symbol sheet More worksheets

Variants as SVG line art: PNP transistorPNP transistor, N-channel MOSFETN-channel MOSFET, P-channel MOSFETP-channel MOSFET

Free to reuse under CC BY 4.0. Credit: Circuit Symbols (circuitsymbols.com). Licence and credit

Sources

15 sources, numbered as cited
  1. ModEL — Bipolar Junction Transistors, simplified tutorial and §4.2 (terminal roles)

    Tony R. Kuphaldt, retrieved 2026-09-22.

  2. Lessons In Electric Circuits, Vol. V — §9, Circuit Schematic Symbols (pp. 130–139)

    Tony R. Kuphaldt, retrieved 2026-09-22.

  3. ModEL — Field-Effect Transistors, §4.3 and §6.2 (body, channel and symbol alternatives)

    Tony R. Kuphaldt, retrieved 2026-09-22.

  4. ModEL — Bipolar Junction Transistors, §4.3 note 8 (emitter arrow direction, p. 32)

    Tony R. Kuphaldt, retrieved 2026-09-23. an outward-pointing arrow signifies an NPN transistor … while an inward-pointing arrow signifies a PNP transistor

  5. Design to Manufacturing Standards — Reference Designators (slide 33)

    Dieter Bergman, IPC, retrieved 2026-09-22. BT battery … CB circuit breaker … DS display, lamp, light emitting diode … RT thermistor

  6. E84 — Bipolar Junction Transistor: terminals and optional symbol enclosure

    Ruye Wang, Harvey Mudd College, retrieved 2026-09-22.

  7. ModEL — Bipolar Junction Transistors, simplified tutorial (current directions and the emitter arrow, p. 20)

    Tony R. Kuphaldt, retrieved 2026-09-23. In all cases the base and and collector currents “mesh” together to match the direction of the emitter’s arrow symbol.

  8. Lessons In Electric Circuits, Vol. III — §2.8, bipolar junction transistors (emitter arrow, p. 63)

    Tony R. Kuphaldt, retrieved 2026-09-23. It points in the same direction as the anode arrow for a junction diode, against electron current flow.

  9. Electrical Schematics, §§1.3.1–1.3.5 — nodes, crossings, references and congruent drawings

    Tufts University, retrieved 2026-09-22.

  10. ModEL — PN Junctions and Diodes, §§2.3–2.7 (bias and diode variants)

    Tony R. Kuphaldt, retrieved 2026-09-22.

  11. ModEL — Components and Symbols, §3.16 (diodes, p. 29)

    Tony R. Kuphaldt, retrieved 2026-09-23. Current (pointed in “conventional flow” notation) can only pass through the diode in the direction of the diode’s arrowhead symbol.

  12. Diodes — terminal polarity, ideal and offset models (pp. 1–2, 7–10)

    MIT OpenCourseWare — Chaniotakis and Cory, retrieved 2026-09-22.

  13. ModEL — Semiconductor Logic Gates, §2.1 (schematic versus package pinout, p. 8)

    Tony R. Kuphaldt, retrieved 2026-09-23. Research a manufacturer’s datasheet for this logic gate IC to see the “pinout” diagram showing which pins on the IC package connect to which inverter gate terminals inside.

  14. ModEL — Electromechanical Relays, §§3.2–3.3 and §5.1 (normal and present contact status)

    Tony R. Kuphaldt, retrieved 2026-09-22.

  15. ModEL — Transistor Switching Circuits, §§3.1–3.4 (cutoff and saturation)

    Tony R. Kuphaldt, retrieved 2026-09-22.