A mathematical model of a high-sensitivity pressure sensor with a novel electrical circuit utilizing piezosensitive transistor differential amplifier with negative feedback loop (PDA-NFL) is presented. Circuits utilizing differential transistor amplifiers based on vertical n-p-n and lateral p-n-p transistors are analyzed and optimized for sensitivity to pressure and stability of output signal in operating temperature range. Parameters of fabrication process necessary for modeling of I-V characteristics of transistors are discussed. The results of the model are sufficiently close to the experimental data.