The proof of concept of a new extended-gate pH sensor, developed on an industrial ultrathin body and buried oxide (UTBB) fully-depleted silicon-on-insulator (FDSOI) transistor, is reported. The strong electrostatic coupling between the front gate and back gate of UTBB FDSOI devices provide a signal amplification opportunity for sensing applications. On the other hand, the biasing capability through a capacitive divider circuit of a floating gate ISFET offers an ample advantage for fabrication of stable and CMOS compatible solid state chemical sensors. In addition, the deep downscaling of the state-of-the-art devices enables it to be sensitive at single-charge-resolution. By integrating aluminum oxide (Al₂O₃) for the pH sensing purpose, we obtained an extended-gate mode ISFET having a sensitivity of 475 mV/pH, which is superior to state-of-the-art low-power ISFETs.