Abstract: A semiconductor device comprising a pn junction diode and a method of making the same. The device includes a semiconductor substrate having a first conductivity type. The device also includes a buried oxide layer located in the substrate. The device further includes a semiconductor region having a second conductivity type extending beneath the buried oxide layer to form a pn junction with a semiconductor region having the first conductivity type. The pn junction is located beneath the buried oxide layer and extends substantially orthogonally with respect to a major surface of the substrate. The device also includes a field plate electrode comprising a semiconductor region located above the buried oxide layer for modifying an electric field at the pn junction by application of a potential to the field plate electrode.