A multidisciplinary team published a conformal, ultrathin crystalline‑silicon Hall sensor array that enables early‑stage monitoring of three‑dimensional tumor tissues. Reported in npj Flexible Electronics, the device combines flexible semiconductor sensor arrays with signal processing to track tumor growth dynamics in vitro and promises non‑invasive monitoring interfaces for tissue models. Hall sensors detect magnetic fields; here an ultrathin array is repurposed for high‑resolution bioelectronic monitoring of 3‑D tumor constructs. The work demonstrates a platform that could accelerate preclinical testing of therapies and longitudinal tumor biology studies when integrated with organoid or microtissue systems.