There are disclosed herein various implementations of composite semiconductor devices with active oscillation 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 may be configured to include one or both of a reduced output resistance due to, for example, a modified body implant and a reduced transconductance due to, for example, a modified oxide thickness to cause a gain of the composite semiconductor device to be less than approximately 10,000.