High-performance and low-power flexible Schottky diode-based hydrogen sensor was developed. The sensor was fabricated by releasing Si nanomembrane (SiNM) and transferring onto a plastic substrate. After the transfer, palladium (Pd) and aluminum (Al) were selectively deposited as a sensing material and an electrode, respectively. The top down fabrication process of flexible Pd/SiNM diode H-2 sensor is facile compared to other existing bottom-up fabricated flexible gas sensors while showing excellent H-2 sensitivity (Delta I/I-0 > 700-0.5% H-2 concentrations) and fast response time (tau(10-90) = 22 s) at room temperature. In addition, selectivity, humidity, and mechanical tests verify that the sensor has excellent reliability and robustness under various environments. The operating power consumption of the sensor is only in the nanowatt range, which indicates its potential applications in low-power portable and wearable electronics.