GaN-based field effect transistor of a normally-off type

A GaN-based field effect transistor comprising:

• a source electrode and a drain electrode;
• a channel portion made of a first GaN-based semiconducting material that is an i-GaN-based semiconducting material or a p-GaN-based semiconducting material, the channel portion being so formed as to be electrically connected to said source and drain electrodes;
• first and second electron supply portions made of second GaN-based semiconducting material having greater bandgap energy than said first GaN-based semiconducting material, the first and second electron supply portions being joined to said channel portion and located separately from each other;
• contact layers made of a third GaN-based semiconducting material having bandgap energy smaller than or equal to said first GaN-based semiconducting material, said contacting layers being located between said channel portion and the source electrode and between said channel portion and the drain electrode, respectively;
• an insulating layer overlaid on a surface of said channel portion, which spreads between said first and second electron supply portions;
• and
• a gate electrode disposed on said insulating layer.