Method of producing a semiconductor device

A method of producing a semiconductor device comprising the steps of:

• preparing a stacked structure having an InP substrate, an intrinsic channel layer formed on said InP substrate, a first doped GaAsSb carrier supply layer formed on said intrinsic channel layer, an etching stopper layer formed on said first doped GaAsSb carrier supply layer, and a second doped GaAsSb carrier supply layer formed on said etching stopper layer;
• forming an isolation region which extends from a surface of said second doped GaAsSb carrier supply layer to said intrinsic channel layer, said isolation region isolating the semiconductor device into first and second device regions;
• forming first and second source electrodes, first and second drain electrodes and a first gate electrode on said second doped GaAsSb carrier supply layer, said first source electrode, said first drain electrode and said first gate electrode being formed in said first device region;
• selectively etching said second doped GaAsSb carrier supply layer to form an opening which extends from the surface of said second doped GaAsSb carrier supply layer to a surface of said etching stopper layer, said etching stopper layer having an etching rate which is small compared to an etching rate of said second doped GaAsSb carrier supply layer;
• and
• forming a second gate electrode on said etching stopper layer within said opening, said second source electrode, said second drain electrode and said second gate electrode being formed in said second device region.