A MEMS sensor comprises a vibrating sensing structure formed from a semiconductor substrate layer (50). The semiconductor substrate layer (50) is mounted on a pedestal comprising an electrically insulating substrate layer (52) bonded to the semiconductor substrate (50) to form a rectangular sensor chip. The pedestal further comprises an electrically insulating spacer layer (54) for mounting the sensor chip to a housing. The electrically insulating spacer layer (54) is octagonal. When the vibrating sensing structure is excited into a cos 2θ vibration mode pair, the quadrature bias arising from any mode frequency split is not affected by changes in temperature as a result of the octagonal spacer layer (54).