A new structure of Schottky diode using the p(+)-polycrystalline silicon (polysilicon) diffused-guard-ring is proposed. For 950 degrees C with 30 min annealing condition, the diode gives a nearly ideal J-V characteristic with a high reverse breakdown voltage (148 V) and a low reverse leakage current density (8.4 mu A/cm(2)). The guard-ring structure prevents the premature breakdown; the polysilicon layer prevents the surface leakage. It was also found that the more the driving time of furnace, the higher the breakdown voltage of the Schottky diode. The breakdown characteristic of a Schottky diode was shown to be closely related with the diffusion length of the boron ions being inside the Si wafer. The electrical characteristics of the p(+)-polysilicon diffused-guard-ring Schottky device was compared with those of the conventional diffused-guard-ring sample.