- Multicomponent nanoparticles represent a new approach for creating smart materials, requiring the development of the growth of different material types on one particle. Here, we report the synthesis of asymmetric metal–semiconductor heterostructures where gold is grown on one side of CdSe nanocrystal quantum rods and dots, creating nanostructures offering intrinsic asymmetry for diverse device functionalities such as diode elements, along with one-sided chemical accessibility through the gold tips. Surprisingly, one-sided growth is preceded by two-sided growth and is generally observed in different particle shapes. Theoretical modelling in a lattice-gas model and experimental analysis show that a ripening process drives gold from one end to the other, transforming two-sided growth to one-sided growth. Ripening is therefore occurring on the nanostructure itself, leading to a phase-segregated structure. This thereby extends the realm of ripening phenomena and their significance in nanostructure synthesis, in particular for nanocrystals composed of different materials.