Conductivity modulated field effect transistor with optimized anode emitter and anode base impurity concentrations

A conductivity modulated semiconductor device comprising:

• a semiconductor substrate of a first conductivity type;
• a first epitaxial semiconductor layer of a second conductivity type which is formed on said semiconductor substrate and has an amount of impurities per unit area of between 5.times.10.sup.13 cm.sup.-2 and 1.times.10.sup.15 cm.sup.-2 ;
• a second epitaxial semiconductor layer of the second conductivity type which has an impurity concentration lower than that of said first epitaxial semiconductor layer and is formed on said first epitaxial semiconductor layer;
• at least one first semiconductor region of the first conductivity type formed in a surface area of said second epitaxial semiconductor layer;
• at least one second semiconductor region of the second conductivity type formed in a surface area of said first semiconductor region;
• a gate electrode formed on an insulation layer over the surface area of said first semiconductor region which lies between said second epitaxial semiconductor layer and said second semiconductor region;
• a source electrode formed in contact with said first and second semiconductor regions;
• and
• a drain electrode formed in contact with said semiconductor substrate.