We demonstrate a new strategy to bond nanowires (NWs) using diffusion bonding of gold (Au). The strategy was used to form very large scale, electrically interconnected 3D NW networks composed of both homogeneous and heterogeneous (multisegmented) NWs. The size of the networks ranged from tens of micrometers to millimeters. We have measured the electrical characteristics of the networks and explored one application of the networks in 3D spatial chemical sensing.