Disclosure includes a normally-off field-effect semiconductor device and the fabrication method thereof. An antigrowth portion is formed on a template. A first semiconductor layer and a second semiconductor layer on the template form two heterojunctions for creating two-dimensional electron gas regions, while a heterojunction-free area defined by the antigrowth portion separate the heterojunctions. A dielectric layer is on the second semiconductor layer and above the antigrowth portion. Two channel electrodes formed on the second semiconductor layer are electrically coupled to the two-dimensional electron gas regions respectively. A gate electrode on the dielectric layer and above the antigrowth portion is used for control of conduction between the channel electrodes.