A thermal sensor structure having one level for an infrared detecting pixel including the sensor associated electronics. The electronics displace a small area thereby having little effect on the fill area of the pixel relative to a level having no pixel electronics. That level has thermally isolation for the substrate through the limited structural attachment to the substrate because of the access vias to the silicon. It has additional isolation because of a pit of removed silicon from the substrate below that one level. The thermal sensor may have an array with a large number of pixels having the one level for the pixels and electronics structure.