In this work, we present a new device concept for compact high-voltage sensing with high-impedance input port, consisting of an AlGaN/GaN high-electron-mobility channel controlled by trapped carriers generated by a metallic electrode. The high-voltage applied to the metallic electrode is determined by measuring the current of the biased high electron-mobility channel. This approach replaces high-voltage probing with low-current measurement and gives a complete isolation between the high-voltage node and the sensing point. Increasing the electrode-to-channel distance in the device leads to a larger measurable voltage range. The device sensitivity can be increased by decreasing the electrode-to-channel distance or by applying a larger bias to the channel. Devices with extremely large input resistance of > 100 GΩ in the sensitive region, along with 2 kV breakdown voltage were fabricated in small dimensions of 50 μm x 50 μm. The high breakdown field of GaN (~3 MV/cm), as a wide-bandgap material, makes it possible to design and fabricate devices based on this topology for future on- and off-chip high-voltage sensing, providing extremely large input resistances which cannot be achieved by conventional methods.