A semiconductor device has an element substrate including a semiconductor layer
of a first conductivity type being formed over a semiconductor substrate with a
dielectric film interposed therebetween. A groove is formed in the element substrate
with a depth extending from a top surface of the semiconductor layer into the dielectric
film, the groove having a width-increased groove portion in the dielectric film
as to expose a bottom surface of the semiconductor layer. An impurity diffusion
source is buried in the width-increased groove portion to be contacted with the
bottom surface. A transistor is formed to have a first diffusion layer being formed
through impurity diffusion from the impurity diffusion source to the bottom surface
of the semiconductor layer, a second diffusion layer formed through impurity diffusion
to the top surface of the semiconductor layer, and a gate electrode formed at a
side face of the groove over the impurity diffusion source with a gate insulation
film between the side face and the gate electrode.
