Bipolar transistor symbol

A line with two angled leads inside a circle, one carrying an arrow.

Also known as: Transistor symbol, BJT symbol, NPN symbol, PNP symbol

Engineering & technicalScientificQuiet profile

Meanings

A bipolar transistor is drawn as a vertical bar with two angled leads, one of which carries an arrow. The arrow's direction is the whole content of the symbol: pointing out means NPN, pointing in means PNP, and nothing else on the page distinguishes them.

Common modern usageVerified fact
Marks a bipolar junction transistor: a three-terminal component in which a small base current controls a much larger current between collector and emitter.
Contexts: Electrical equipment
Common modern usageVerified fact
Names its three terminals base, collector and emitter. The base is the lead meeting the flat bar; the emitter is the lead carrying the arrow.
Contexts: Electrical equipment
Common modern usageVerified fact
Distinguishes NPN from PNP solely by the emitter arrow's direction — pointing away from the base for NPN, toward it for PNP. Substituting one for the other in a circuit does not work.
The single most consequential arrow in schematic reading, and the one most often misread.
Contexts: Electrical equipment
Common modern usageCommon usage
Is drawn with or without an enclosing circle depending on house style; the circle historically indicated a discrete packaged device rather than one formed on an integrated circuit.
Contexts: Electrical equipment

Visual description

A short vertical bar with a wire meeting its middle from the left, and two wires leaving its right side at opposing angles, the lower one carrying a small arrowhead; often enclosed in a circle.

A fuller structured visual breakdown is not yet documented for this symbol.

Confidence

IdentityHigh confidence: High confidence because the identity is documented in encyclopedic references, but multiple independent sources agree.
Historical originLow confidence: Low confidence because the historical origin is documented in encyclopedic references, but only a single source has been found so far, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is documented in encyclopedic references, but multiple independent sources agree.
Visual matchHigh confidence: High confidence because the visual match is documented in encyclopedic references, but multiple independent sources agree.

Sources

Bipolar junction transistor
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for what the component is, how its symbol is conventionally drawn, and where the ANSI and IEC conventions differ. Not used for any claim about the text of IEC 60617, which is paywalled and was not consulted.
Electronic symbol
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for what the component is, how its symbol is conventionally drawn, and where the ANSI and IEC conventions differ. Not used for any claim about the text of IEC 60617, which is paywalled and was not consulted.
Circuit diagram
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for what the component is, how its symbol is conventionally drawn, and where the ANSI and IEC conventions differ. Not used for any claim about the text of IEC 60617, which is paywalled and was not consulted.

Last reviewed 2026-07-31

Part of

Circuit and schematic symbols

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Meanings

Common modern usageVerified fact

Marks a bipolar junction transistor: a three-terminal component in which a small base current controls a much larger current between collector and emitter.

Contexts: Electrical equipment

Common modern usageVerified fact

Names its three terminals base, collector and emitter. The base is the lead meeting the flat bar; the emitter is the lead carrying the arrow.

Contexts: Electrical equipment

Common modern usageVerified fact

Distinguishes NPN from PNP solely by the emitter arrow's direction — pointing away from the base for NPN, toward it for PNP. Substituting one for the other in a circuit does not work.

The single most consequential arrow in schematic reading, and the one most often misread.

Contexts: Electrical equipment

Common modern usageCommon usage

Is drawn with or without an enclosing circle depending on house style; the circle historically indicated a discrete packaged device rather than one formed on an integrated circuit.

Contexts: Electrical equipment

Confidence

IdentityHigh confidence: High confidence because the identity is documented in encyclopedic references, but multiple independent sources agree.
Historical originLow confidence: Low confidence because the historical origin is documented in encyclopedic references, but only a single source has been found so far, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is documented in encyclopedic references, but multiple independent sources agree.
Visual matchHigh confidence: High confidence because the visual match is documented in encyclopedic references, but multiple independent sources agree.

Sources

Bipolar junction transistor
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for what the component is, how its symbol is conventionally drawn, and where the ANSI and IEC conventions differ. Not used for any claim about the text of IEC 60617, which is paywalled and was not consulted.
Electronic symbol
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for what the component is, how its symbol is conventionally drawn, and where the ANSI and IEC conventions differ. Not used for any claim about the text of IEC 60617, which is paywalled and was not consulted.
Circuit diagram
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for what the component is, how its symbol is conventionally drawn, and where the ANSI and IEC conventions differ. Not used for any claim about the text of IEC 60617, which is paywalled and was not consulted.

Last reviewed 2026-07-31