GaN-BASED FIELD EFFECT TRANSISTOR

A GaN-based field effect transistor, comprising:

• a channel layer composed of p-type GaN-based compound semiconductor;
• a drift layer formed on said channel layer, composed of n-type GaN-based compound semiconductor and having a concave recess that reaches said channel layer at part thereof;
• source electrode and drain electrode formed on said drift layer so as to be electrically connected with said drift layer and so as to interpose said recess;
• an insulating film formed on the inner surface of said recess and on the surface of said drift layer;
• and
• a gate electrode formed on said insulating film and having a field plate portion;
• wherein said drift layer has a reducing surface field region composed of n-type GaN-based compound semiconductor whose sheet carrier density is more than 5×1013 cm−2 and less than 1×1014 cm−2 between said recess and said drain electrode and thickness of said insulating film formed on said reducing surface field region of said drift layer is 300 nm or more.