MOSFET terminal count – practical devices: How many terminals does a MOSFET present, considering that in discrete devices the body/substrate may be internally tied to the source?

Introduction / Context:
Understanding how many terminals a MOSFET exposes guides correct biasing and measurement. While the MOS structure has gate, source, drain, and body (substrate), packaging and internal connections vary.

Given Data / Assumptions:

• Discrete power MOSFETs often short the body to source internally.
• IC processes may bring the body out as a separate terminal in 4-terminal FETs.
• We count external, usable terminals.

Concept / Approach:
A MOSFET fundamentally has four regions: gate (G), drain (D), source (S), and body (B). In many discrete devices, B is internally tied to S → the package exposes three pins (G, D, S). Some specialty or IC devices provide a separate body connection → four terminals.

Step-by-Step Solution:
Identify intrinsic terminals: G, D, S, B.Check packaging: B tied to S → 3 leads; B separate → 4 leads.Hence: “3 or 4.”

Verification / Alternative check:
Datasheets show pinouts; many TO-220/TO-247 parts are 3-lead, while small-signal MOSFET arrays or IC processes sometimes present 4 terminals.

Why Other Options Are Wrong:
“2 or 3” ignores the body connection reality; two-terminal operation is not a MOSFET package convention.

“Only 3” or “only 4” excludes common variants.

“5” is not standard for a single MOSFET.

Common Pitfalls:
Assuming the body diode orientation without confirming body–source tie; incorrect assumptions can affect reverse conduction behavior.

Final Answer:
3 or 4