The one-paragraph version
A charger converts wall AC into the DC voltages phones and laptops negotiate. The switching transistors that do the heavy lifting were historically silicon. Gallium nitride switches faster with lower losses at the same rating, so a GaN charger can run a higher switching frequency, shrink its magnetics, and waste less energy as heat. The visible result is the format change buyers know: a 65W GaN unit is pocket-sized where a silicon 65W unit was a brick.
Why faster switching shrinks the box
A charger's size is set mostly by its transformer and capacitors, and both shrink as switching frequency rises. GaN transistors tolerate those higher frequencies efficiently; silicon designs pushed the same way would overheat. Higher efficiency also means less heat to shed, so the enclosure needs less surface area - the two effects compound, which is why the size gap between GaN and silicon grows with wattage. At 20W the difference is a smaller cube; at 100W it is the difference between a travel accessory and a desk brick.
What GaN does not change
The charging protocols are identical: a GaN charger speaks USB Power Delivery and PPS exactly as a silicon one does, and the device - not the charger - decides how much power to draw. GaN also does not repeal thermal physics: a sealed 100W charger in a hot room will still throttle. When you compare suppliers, the honest GaN evidence is in the published profiles - full PD steps, PPS ranges and multi-port splits - not in the material claim itself. The manufacturer's range on this site publishes those profiles for all 50 GaN models, from the 20W mini series to the 100W series.
GaN I, II, III - should buyers care?
Generational labels describe successive GaN device and integration designs; each generation tends to buy a few points of efficiency or a smaller footprint at the same wattage. For a sourcing decision the generation label matters less than the measured outputs and the thermal behaviour of samples. Treat the label as a datasheet footnote, not a tier. The companion guide, GaN vs silicon chargers, puts the two side by side for the same wattages.