Piezoresistive strain gauges are a semiconductor material which changes in resistance when the material stretched or compressed.
Typically they are made from N or P type silicon and are either manufactured as separate elements for bonding to the surface of a sensing diaphragm or embedded into a silicon chip sensing diaphragm via a ion implantation process.
The main benefit of piezo-resistive strain gages is that they have a much higher gauge factor than bonded foil strain gauges, which results in a significantly higher mV/V sensitivity and less noisy output signal.
The ion implanted form of piezoresistive strain gauges have a more stable performance than the bonded type. The gauges are basically the same material which has been implanted with ions, so the boundary between the two materials is considered to be a perfect bond. The semiconductor strain gauges are isolated from the surrounding semiconductor substrate by creating a applying a reverse voltage between the P and N type silicon which provides electrical isolation for the strain gauge region.
There is also no need to apply additional inelastic materials such as film coatings and adhesives which are used on the bonded film strain gauges, which tend to degrade over time causing changes to the characteristics of the strain gauge.