MEMS sensors are promising for Energy Efficient Building (EeB) because of the potential low cost and low power consumption. Various flow sensors based on MEMS technology have been fabricated. In this work, we designed and fabricated a polysilicon micro hot-wire flow sensor using a commercial 0.35μm 2P4M CMOS technology followed by post-CMOS processing. A post-CMOS MEMS process for a 1.5mm×1.5mm sensor chip using Deep Reactive Ion Etch (DRIE) and spray coating was utilized to finish the fabrication. The fabricated flow sensor was characterized at different flow rates. The fabricated sensor with a dimension of 300μm×2μm×3.76μm demonstrated a sensitivity of 23.87 mV/(m/s) and power consumption of 0.79 mW at Uin =5m/s. The experiment results were consistent with the theoretical prediction and the best results showed an average error of only 5%.