Abstract The emerging multi-channel GaN architecture offers great opportunities in high-performance devices, whose performance is fundamentally determined by the density and distribution of electrons among the parallel multi-channels. In this work, we present approaches to design multi-channel GaN heterostructures based on a proposed physical-based model and experimental results. The model presents excellent accuracy based on comparisons with TCAD and experimental results. Impacts of key designing parameters upon the two-dimensional electron gas density and the distribution of electrons were systematically investigated within undoped and doped multi-channels, presenting a criterion to determine the maximum channel thickness and evaluate the multi-channel design, and offering a design guideline to design and optimize a multi-channel-GaN heterostructure for a given targeted application.