An improved Schottky barrier device and the method of its manufacture are disclosed. The device comprises a semiconductor layer of first conductivity type, an insulating layer covering one face of the semiconductor layer and having an opening therein, a conductor layer covering the semiconductor layer where it is exposed by the opening and forming a Schottky contact with the semiconductor layer, a first region of opposite conductivity type within the semiconductor layer generally beginning where the conductor layer meets the insulating layer and extending below the conductor layer, and a second region of opposite conductivity type within the semiconductor layer generally beginning where the conductor layer meets the insulting layer and extending below the insulating layer, the second region having a lower concentration of dopants, so that there is formed an asymmetric guard ring, and the opening in the insulating layer has an edge which is bevelled with a slope of between 0.1 and 0.4.