Patent ID: 7208777

Claim:
A field-effect semiconductor device comprising: a channel layer; a contact layer; a semiconductor structure having an electron-affinity different from those of the channel layer and the contact layer and formed between the channel layer and the contact layer, the semiconductor structure having a first junction face between the semiconductor structure and the channel layer and having a second junction face between the semiconductor structure and the contact layer; an ohmic electrode formed on the contact layer; and a Schottky electrode formed on the semiconductor structure; wherein both of the first junction face and the second junction face are iso-type heterojunctions; the semiconductor structure is composed of a single material and includes at least three semiconductor layers; the first junction face between the channel layer and the semiconductor structure and the second junction face between the contact layer and the semiconductor structure are iso-type heterojunctions; the channel layer and the semiconductor structure at the first junction face are each formed of doped layers; the contact layer and the semiconductor structure at the second junction face are each formed of doped layers; and the semiconductor structure includes an undoped layer intermediate the dosed layers thereof.