The electronic transport properties of zigzag phosphorene nanoribbon (ZPNR) homostructures are investigated using density functional theory calculations and the nonequilibrium Green’s function technique. The proposed devices have simple constructions but exhibit robust negative differential resistance (NDR) as well as quite large current, which implies great potential for building nanoelectronic devices. Through the analysis of the electronic structures and transmission spectra, we give a clear physical picture of the NDR mechanism, in which such current–voltage (I–V) behaviors originate from the bias-dependent interaction between the discrete density of states (DOS) peaks of the electrodes and the narrow states around the Fermi level in the scattering region.