Semiconductor device

A semiconductor device includes an insulating layer, a semiconductor layer, and a compound semiconductor stacked layer disposed on a substrate in sequence, a first transistor, a second transistor, an isolation structure, and a conductive structure. The first transistor is disposed in a first element region and includes a first gate, a first source and a first drain disposed on the compound semiconductor stacked layer. The second transistor is disposed in a second element region, and includes a second gate, a second source, and a second drain disposed on the compound semiconductor stacked layer. The isolation structure is disposed between the first transistor and the second transistor. The conductive structure is disposed in the second element region, penetrates the compound semiconductor stacked layer, and electrically connects the semiconductor layer to the second source. There is no electrical connection between the semiconductor layer in the first element region and the first source.