The present invention relates to a MEMS pressure sensor die and its fabrication process. The pressure sensor comprises a chamber inside which a MEMS pressure sensor die is provided. The pressure sensor die comprises a handle, a device layer and a cap all connected together. A silicon oxide layer is formed between the handle and the device layer. Another silicon oxide layer is formed between the device layer and the cap. Recesses are respectively formed on the handle and the cap and face each other. The handle recess and the cap recess are connected to form a cavity. The device layer, which spans the cavity, further comprises a bridge on which a plurality of piezoresistive sensing elements are formed. The present pressure sensor is more immune to temperature effects. It is especially suitable for operating in a high temperature, high pressure environment and is capable of delivering accurate and reliable pressure measurements at low cost.