A high electron mobility transistor (HEMT) device includes at least an AlN nucleation layer, a superlattice composite layer, a GaN electron transport layer, and an AlGaN barrier layer. The superlattice composite layer is disposed on the AlN nucleation layer, and the superlattice composite layer includes a plurality of AlN films and a plurality of GaN films stacked alternately to reduce device stress. The GaN electron transport layer is disposed on the superlattice composite layer, and the AlGaN barrier layer is disposed on the GaN electron transport layer.