We report the electrothermal properties of AAA trilayer on polyethylene terephthalate substrate which allowed the development of low-cost high-performance transparent thin-film flexible heater (TTFFH) using RF magnetron sputtering. The structural, electrical, and optical properties of the AAA trilayer were investigated at different thickness of the Ag interlayer. The AAA trilayer-based TTFFH yielded saturation temperatures beyond 100 degrees C at 10 V at optimized Ag interlayer thickness of 5 nm. The time-dependent temperature profile along with its highly stable and reversible thermal behavior was studied. Most importantly, the AAA trilayer-based TTFFH provides a high-performance alternative to the conventional and expensive ITO electrodes at a much lower cost.