Techniques are provided herein to form gate-all-around (GAA) semiconductor devices utilizing a metal fill in an epi region of a stacked transistor configuration. In one example, an n-channel device and the p-channel device may both be GAA transistors each having any number of nanoribbons extending in the same direction where the n-channel device is located vertically above the p-channel device (or vice versa). Source or drain regions are adjacent to both ends of the n-channel device and the p-channel device. A metal fill may be provided around the source or drain region of the bottom semiconductor device to provide a high contact area between the highly conductive metal fill and the epitaxial material of that source or drain region. Metal fill may also be used around the top source or drain region to further improve conductivity throughout both of the stacked source or drain regions.