A semiconductor structure including a group III-N semiconductor material is disposed on a silicon substrate. A group III-N transistor structure is disposed on the group III-N semiconductor material. A well is disposed in the silicon substrate. The well has a first conductivity type. A doped region is disposed in the well. The doped region has a second conductivity type that is opposite to the first conductivity type. A first electrode is connected to the well of the second conductivity type and a second electrode is connected to the doped region having a first conductivity type. The well and the doped region form a PN diode. The well or the doped region is connected to the raised drain structure of the group III-N transistor.