In urban areas where land is scarce, skyscrapers and high-rise buildings enable homes and businesses to be densely packed into small areas. Now, in a paper presented at the 2025 IEEE International Electron Devices Meeting, Liao et al.1 of Taiwan Semiconductor Manufacturing Company (TSMC) apply this principle to integrated circuits — reporting two logical circuits in which two kinds of transistor are stacked on top of each other. In the decades since transistors were invented, the electronics industry has continuously packed them more densely onto chips, but the physical limitations of conventional transistor materials make it challenging to continue this trajectory. Liao and colleagues’ work shows that, with innovations in materials and device design, it is still possible to develop ways to optimize chip space.…