[en] In recent years, significant progress has been made on Complementary Metal Oxide Semiconductor (CMOS) devices, which have been proposed as X-ray imaging spectroscopes for future space astronomy missions. We tested a newly developed backside-illuminated scientific CMOS (BSI sCMOS) device, which is treated as a soft X-ray imaging spectroscopy. This BSI sCMOS has an array of 2048×2048 pixels with a pixel size of 11 μm and an epitaxial thickness of 3.6 μm. It is an active pixel sensor with fast readout, low power consumption and low readout noise. We investigated the performance of this BSI sCMOS as a soft X-ray detector. The energy resolution reaches 192 eV at 5.9 keV near room temperature. When the detector is cooled down to −20^oC, the results show the readout noise to be approximately 1.5 e⁻, the dark current to be 159 e⁻/pixel/s, and the energy resolution to be 187 eV (3.2%) at 5.9 keV . Meanwhile, the soft X-rays down to the carbon line (277 eV) can be clearly identified.