There are disclosed herein various implementations of composite III-nitride semiconductor devices having turn-on prevention control. In one exemplary implementation, a normally OFF composite semiconductor device comprises a normally ON III-nitride power transistor 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 is configured to have a noise-resistant threshold voltage to provide the turn-on prevention control for the normally OFF composite semiconductor device by preventing noise current from flowing through a channel of the normally ON III-nitride power transistor in a noisy system.