Patent ID: 8035138

Claim:
A junction field effect transistor comprising: a first conductivity type semiconductor substrate; a first conductivity type lower epitaxial layer formed on the semiconductor substrate; a second conductivity type epitaxial layer, providing a channel region, formed on the first conductivity type lower epitaxial layer; a first conductivity type upper epitaxial layer formed on the second conductivity type epitaxial layer such that the second conductivity type epitaxial layer is sandwiched between the first conductivity type lower epitaxial layer and the first conductivity type upper epitaxial layer; a second conductivity type source region which penetrates the first conductivity type upper epitaxial layer in a layer thickness direction thereof and is connected to the second conductivity type epitaxial layer, the second conductivity type source region being formed such that a deepest portion thereof reaches the second conductivity type epitaxial layer without penetrating the second conductivity type epitaxial layer; a second conductivity type drain region which is spaced from the source region, penetrates the first conductivity type upper epitaxial layer in the layer thickness direction, and is connected to the second conductivity type epitaxial layer, the second conductivity type drain region being formed such that a deepest portion thereof reaches the second conductivity type epitaxial layer without penetrating the second conductivity type epitaxial layer; a source electrode connected to the source region; a drain electrode connected to the drain region; a gate electrode electrically connected to the first conductivity type upper epitaxial layer between the source region and the drain region; and a first conductivity type region penetrating the second conductivity type epitaxial layer, the first conductivity type region electrically connecting the first conductivity type lower epitaxial type layer and the first conductivity type upper epitaxial layer, wherein the source region has a width in a direction orthogonal to a lamination direction which is larger in a vicinity of the second conductivity type epitaxial layer than in the first conductivity type upper epitaxial layer.