There are disclosed herein various implementations of composite semiconductor devices including a voltage protected device. In one exemplary implementation, a normally OFF composite semiconductor device comprises a normally ON III-nitride power transistor having a first output capacitance, and a low voltage (LV) device cascoded with the normally ON III-nitride power transistor to form the normally OFF composite semiconductor device, the LV device having a second output capacitance. A ratio of the first output capacitance to the second output capacitance is set based on a ratio of a drain voltage of the normally ON III-nitride power transistor to a breakdown voltage of the LV device so as to provide voltage protection for the LV device.