Stacked semiconductor die assemblies with die substrate extensions are disclosed herein. In one embodiment, a semiconductor die assembly can include a package substrate, a first die mounted to the package substrate, and a second die mounted to the first die. The first die includes a first die substrate, and the second die includes a second die substrate attached to the first die substrate. At least one of the first and second dies includes a semiconductor substrate and a die substrate extension adjacent the semiconductor substrate. The die substrate extension comprises a mold material that at least partially defines a planform.