Effective width (W_eff): definition

Beginner

How much of the channel’s edge the gate touches, added up. More of it lets more electricity flow.

Novice

The total width of channel surface the gate controls, which sets how much current a transistor can carry. For a flat transistor it is the drawn width; for a fin it is two sides plus the top; for a nanosheet it is the whole outline of every sheet.

Expert

Gated perimeter per device: $W$ (planar), $n_{\mathrm{fin}}(2H_{\mathrm{fin}} + W_{\mathrm{fin}})$ (tri-gate FinFET), $n_{\mathrm{sh}} \cdot 2(w + t)$ (nanosheet). Drive current and intrinsic gate capacitance both scale with it, so the useful figure is $W_{\mathrm{eff}}$ per footprint.