There is a great demand to develop high-performance hydrogen sulfide (H₂S) sensors, especially at the trace level for environmental protection, human healthcare, and food freshness monitoring. To this end, cellulose nanofiber (CNF)-templated CuO (CuO-C) was decorated with tungsten disulfide (WS₂) nanosheets (W-Cu-C) as the sensing layer of chemiresistive microelectromechanical system (MEMS) sensors for H₂S recognition in this work. As compared to pristine CuO counterparts at 160.5 °C, the as-prepared W-Cu-C-10 sensors delivered a 30-fold enhanced response of 37 toward 0.5 ppm H₂S at a lower optimal operation temperature of 100.1 °C. Moreover, a fast response/recovery speed of 37.2/33.9 s toward 0.5 ppm H₂S and excellent long-term stability and selectivity were achieved. Compared with existing research and commercial products, the W-CU-C-10 sensors exhibited the remarkable superiorities of high sensitivity, the lowest detection limit of 200 ppb, and ultralow power consumption (8 mW). Also, the sensor showcased a nice on-site application potential for evaluating eggs’ freshness. The proposed W-Cu-C-10 sensors probably pave a new avenue for designing high-sensitivity and energy-efficient future H₂S sensors, especially in the fields of portable and wearable detection systems as well as Internet of Things.