The ability to control the charge carrier transport in the colloidal NC assemblies is fundamental for altering their electronic and optical properties for the desired applications. While surface doping and ligand manipulations have been very effective, they generally suffer from the sample-to-sample variability and insufficient long-term retention of the surface stoichiometry due to environmental effects. Wherever possible and applicable, the formation of a more stable core-shell morphology wherein shell acts as a dopant and carrier-regulating region is preferred. For many applications in devices where charge carrier transport functionality is one of the most prominent, the role of shells in the core@shell NCs are still not well understood. The shell might not only provide the NCs with better stability but may also result in vastly different physical properties of the overall heterostructure. Here we demonstrate a strategy to render the solids of narrow-bandgap NC assemblies exclusively electron-transporting by creating a type-II heterojunction via shelling. Electronic transport of molecularly cross-linked PbTe@PbS core@shell NC assemblies is measured using both a conventional solid gate transistor and an electric-double-layer transistor. The transport characteristics are compared with those of core-only PbTe NCs. In contrast to the ambipolar characteristics demonstrated by many narrow-bandgap NCs, the core@shell NCs exhibit exclusive n-type transport, i.e., drastically suppressed contribution of holes to the overall transport. The PbS shell that forms a type-II heterojunction assists the selective carrier transport by heavy doping of electrons into the PbTe-core conduction level and simultaneously strongly localizes the holes within the NC core valence level. Any efforts to use various kinds of hole dopants are not strong enough to counteract the influence of the shell. Furthermore, the use of electric-double-layer transistor to scan broadly the Fermi level provides a clear pictorial related to the absence of hole transport and the enhanced electron transport. This strongly enhanced n-type transport makes these core@shell NCs suitable for applications where ambipolar characteristics should be actively suppressed to enhance their performance, in particular, photodetectors, thermoelectric devices and the selective electron-transporting layer in solar cells and the other optoelectronic devices.