We present the design, fabrication, and characterization of a thermoelectric IR sensor based on the standard 0.35 µm CMOS process. The sensor features 32 thermopile junctions with centrally located hot ends and a ring-shaped aluminum grating absorber, both configured as suspended structures to enhance thermal isolation and improve temperature sensitivity. The cold ends of the thermopiles are anchored to the silicon substrate to establish a temperature gradient under IR exposure. The device was fabricated through Taiwan Semiconductor Manufacturing Company (TSMC) processes. A two-step post-CMOS etching process—using CF4/O2 and SF6/O2 reactive ion etching—was employed to create cavities beneath the suspended regions, minimizing thermal losses and enhancing output performance. The sensor’s voltage responsivity reached 276 V/W. Additionally, dynamic response testing using a modulated IR source and an optical chopper revealed a response time of 2.2 ms. The proposed sensor demonstrates high sensitivity, fast response, and compatibility with large-scale semiconductor manufacturing.