Conductivity modulated MOSFET

A conductivity modulated metal oxide semiconductor field effective transistor, comprising:

• a semiconductor substrate of a first conductivity type which has first and second surfaces;
• a high resistance semiconductor layer of a second conductivity type which is formed on said first surface of said semiconductor substrate and has a high resistance;
• a base layer of the first conductivity type which is formed in said high resistance semiconductor layer;
• a source layer of the second conductivity type which is formed on said high resistance semiconductor layer and a channel region, said channel region being formed in said base layer between said high resistance semiconductor layer and said source layer;
• a source electrode ohmic-contacting said source layer and said base layer;
• and
• a drain electrode formed on said second surface of said semiconductor substrate;
• wherein when a total channel width within a unit area (1 cm.sup.2) of an active region is W(.mu.m), an area of the high resistance layer which is formed beneath the gate electrode and is in direct contact with the gate insulating film within said unit area of the active region is SG(.mu.m), a perimeter of said area SG within said unit area of the active region is T(.mu.m), a channel length is l(.mu.m) and a thickness of said gate insulating film is d(.mu.m), a condition (W.multidot.SG)/(T.multidot.l.multidot.d)<1.46.times.10.sup.8 is satisfied.