A new pH sensor with high pH sensitivity and linearity is proposed, which is based on an extended gate field effect transistor (EGFET) connected with a hybrid GaN high electron mobility transistor (HEMT) in series with a low-onset-voltage Schottky barrier diode (SBD) on the source side. The pH sensitivity of the proposed sensor is 0.017 A/mm-pH with the linearity of 0.37%. The work is in collaboration with Prof. Zhenchuan Yang