A new CMOS compatible thermopile was designed and fabricated with high fill factor, the floating membrane of the thermopile which we designed was formed by T-shape anisotropic etching window that never be proposed before. The design and fabrication of thermopile sensors are realized by using 1.2 μm CMOSIC technology combined with a subsequent anisotropic frontside etching. Four etching windows with minimum T-shape were opened by the CMOS processes, and then by using N2H4 etching solution the silicon substrate was etched along <100> directions. The T-shape etching windows which proposed in this paper are designed at four quadrant of membrane to form the extended undercut etching area of opened windows of overlap. The floating membrane has a larger area of 1100×1100μm2 and 2 μm thick. Therefore, the area of proposed membrane Ls increased greatly which absorbs more infrared radiation than the conventional design and enhances responsivity very well. A surface morphology measurement of thermopile is implemented to evaluate the influence of residual stress and characterize geometric shape of membrane practically. More careful analysis of surface morphology show the bending of suspension parts has a deviation of responsivity less than 0.167%. For our work, the T-shape structure of thermopile with large absorption area and high performance by using CMOS compatible process is proven to be very successful and easy fabricated.