Method for forming MESFET having T-shaped gate electrode

A method for forming semiconductor device comprising the steps of:

• forming a first insulating film on a compound semiconductor layer served as a channel;
• forming an opening at a gate electrode forming region in said first insulating film;
• depositing a first conductive film in said opening and on said first insulating film, said first conductive film forming a Shotkky barrier on a junction surface with said compound semiconductor layer;
• patterning said first conductive film to leave said first conductive film within and around said opening for forming a gate electrode which has an overhang out of said opening;
• forming a resist film on said first insulating film and said gate electrode, said resist having windows respectively at a source region and a drain region in said compound semiconductor layer;
• removing said first insulating film within a first area between said gate electrode and said source region and a second area between said gate electrode and said drain region without removing a part of said first insulating film under said overhang through said windows of said resist film by isotropical etching;
• forming a second conductive film on said compound semiconductor layer as a source electrode and a drain electrode though said windows at said source region and said drain region, and forming said second conductive film on said resist film;
• lifting off said second conductive film without removing said second conductive film over said source region and said drain region by removing said resist film;
• and
• forming a second insulating film contacting to a side surface of said first insulating film, a surface of said gate electrode and a surface of said compound semiconductor layer.