Internally-shielded microelectronic packages having increased resistances to electromagnetic cross-coupling are disclosed, as are methods for fabricating such microelectronic packages. In embodiments, the internally-shielded microelectronic package includes a substrate having a frontside and a longitudinal axis. A first microelectronic device is mounted to the frontside of the substrate, while a second microelectronic device is further mounted to the frontside of the substrate and spaced from the first microelectronic device along the longitudinal axis. An internal shield structure includes or consists of a shield wall, which is positioned between the first and second microelectronic devices as taken along the longitudinal axis. The internal shield structure is at least partially composed of a magnetically-permeable material, which decreases electromagnetic cross-coupling between the first and second microelectronic devices during operation of the internally-shielded microelectronic package.