
An N.sup.- semiconductor layer is epitaxially grown on an N.sup.+ semiconductor substrate serving as a drain region and overlaid with an N type epitaxial layer. Two opposite P.sup.+ gate regions are disposed in the surface portion of the N layer to define a channel region between them, and an N.sup.+ source region is located above the channel region. That portion of the N layer located between each gate region and the N.sup.- layer has a thickness not smaller than one-half of the channel width o...











