The piezoresistive effect is a change in the electrical resistivity of a material (e.g. semiconductor, metal) when mechanical strain is applied. The electrical resistance change is due to two causes; geometry change and conductivity change of the material. The change in resistance is much more pronounced for semiconductors than for metals.
Semiconductor as a measuring element
Kistler, e.g., offers only piezoresistive pressure sensors based on silicon semiconductors. For this purpose, four Si-resistors are diffused into a semiconductor membrane and connected with another to form a Wheatstone-Bridge. Under the influence of the pressure, the diaphragm deforms, thereby affecting the electrical resistance of the four Si-resistors. The change in resistance is proportional to the applied pressure.
This also means that the differential voltage across the Wheatstone-Bridge is proportional to the applied pressure. The resulting differential voltage can be routed to the electrical connector for evaluation.