A semiconductor device includes a substrate, a first GaN-based high-electron-mobility transistor (HEMT), a second GaN-based HEMT, a first interconnection, and a second interconnection is provided. The substrate has a plurality of first-type doped semiconductor regions and second-type doped semiconductor regions. The first GaN-based HEMT is disposed over the substrate to cover a first region on the first-type doped semiconductor regions and the second-type doped semiconductor regions in the substrate. The second GaN-based HEMT is disposed over the substrate to cover a second region. The first region is different from the second region. The first interconnection is disposed over and electrically connected to the substrate, forming a first interface. The second interconnection is disposed over and electrically connected to the substrate, forming a second interface. The first interface is separated from the second interface by at least two heterojunctions formed in the substrate.