In Early effect:

• The Early effect, is the variation in the effective width of the base in a bipolar junction transistor (BJT) due to a variation in the applied base-to-collector voltage.
• A greater reverse bias across the collector-base junction increases the collector-base depletion width, thereby decreasing the width of the charge carrier portion of the base.
• The collector depletion region also increases under reverse bias, more than does that of the base, because the collector is more heavily doped than the base.
• The principle governing these two widths is charge neutrality.

Base-narrowing has two consequences that affect the current:

1) There is a lesser chance for recombination within the "smaller" base region.

2) The charge gradient is increased across the base, and consequently, the current of minority carriers injected across the collector-base junction increases, which net current is{\displaystyle I_{CB0}} called I_CBO.

The characteristics are shown below: