Multi-channel power devices, in which several AlGaN/GaN layers are stacked to achieve multiple two-dimensional electron gases (2DEGs), have recently led to a significant increase in the device conductivity while maintaining high breakdown voltage, resulting in excellent DC performances. However, their dynamic performance is yet to be demonstrated, especially due to the absence of an effective passivation technique for their 3D structure. Here, we present a surface passivation technology for multi-channel devices based on a conformal deposition of a thin SiO2 interlayer followed by a low-pressure chemical vapor deposition (LPCVD) Si3 N4 layer around the multi-channel fins, which enables to effectively reduce the electron traps both at the AlGaN top surface and at the fin sidewalls. Such an approach led to a significant reduction of the dynamic on-resistance ( RON ) in multi-channel devices under large off-state voltages of 350 V and comparable dynamic performance with passivated single-channel reference devices. This work proves that, in addition to the excellent DC performance, the multi-channel technology can offer reduced current collapse, unveiling the potential of this platform for future power electronic applications.