A sensor comprises a substrate (16) and a sensor element (20) anchored to the substrate (16), the substrate (16) and sensor element (20) being of dissimilar materials and having different coefficients of thermal expansion, the sensor element (20) and substrate (16) each having a generally planar face arranged substantially parallel to one another, the sensor further comprising a spacer (26), the spacer (26) being located so as to space at least part of the sensor element (20) from at least part of the substrate (16), wherein the spacer (26) is of considerably smaller area than the area of the smaller of face of the substrate (16) and that of the sensor element (20).