Branched core/shell bismuth telluride/bismuth sulfide nanorod heterostructures are prepared by using a biomimetic surfactant, L-glutathionic acid. Trigonal nanocrystals of bismuth telluride are encapsulated by nanoscopic shells of orthorhombic bismuth sulfide. Crystallographic twinning causes shell branching. Such heteronanostructures are attractive for thermoelectric power generation and cooling applications.