Abstract: To ascertain the damage mechanism caused by high-energy proton irradiation to AlGaN/GaN power devices of enhanced Cascode structures, we study the radiation effect of enhanced Cascode structure and depletion AlGaN/GaN power devices by using 60 MeV energy protons in this work. In the case of proton injection reaching 1×10¹² p/cm², the experimental results show that the threshold voltage of the Cascode type device is negatively drifted, the transconductance decreases, and the peak leakage current increases. The threshold voltage decreases from 4.2 V to 3.0 V, with a decrement of 1.2 V, and the peak transconductance value decreases from 0.324 S/mm to 0.260 S/mm, with a decrement of about 19.75%. There is no significant change after the conventional depleted AlGaN/GaN device has been irradiated. The Cascode-type AlGaN/GaN power device is more sensitive to proton irradiation than the depletion-type AlGaN/GaN device. The Cascode-type device is sensitive to proton irradiation because of its structure connected to a silicon-based MOS tube. Proton irradiation causes the silicon-based MOS gate oxide layer to generate a large amount of net positive charge, induces an ionization damage effect, and causes threshold voltage to negatively drift and the gate leakage current to increase. The equivalent 60 MeV energy protons and cumulative injection of 1×10¹² p/cm² dose of the _^60\rmC\rmo~\rm\gamma radiation device is used to obtain the ionization damage effect. It is found that after being irradiated by the equivalent dose _^60\rmC\rmo~\rm\gamma ray , the device has the threshold voltage decreasing from 4.15 V to 2.15 V, with a negative drift of 2 V; transconductance peak decreases from 0.335 S/mm to 0.300 S/mm, with an approximate decrement of 10.45%. The degradation of the electrical properties of the device after being irradiated by _^60\rmC\rmo~\rm\gamma ray is consistent with the degradation law after being irradiated by high-energy protons. In order to further verify the experimental accuracy and conclusions, the ionization energy loss and non-ionization energy loss induced by radiation in the device are obtained by Monte Carlo simulation. The simulation results show that the ionization energy loss induces silicon-based MOS to generate oxide trap charge and interfacial state trap charge, which is mainly responsible for the performance degradation of AlGaN/GaN HEMT power devices with enhanced Cascode structure.