We give overview and the current status of the development of the Soft X-ray Imager (SXI) onboard the NeXT satellite. SXI is a back-illuminated supportless CCD (a combination of "back-illuminated CCD" and "supportless CCD") whose imaging area and the supportless region are 42 × 42mm2 and 30mmφ respectively. The goal of the thickness of the depletion layer is 300μm, which enables us to cover the energy range of 0.3 - 25 keV. The evaluation model 'CCD-NeXT1' with the size of 24 × 48mm2 shows no performance change due to the thinning process. The test model of P-channel CCD was confirmed to have high quantum efficiency above 10 keV with an equivalent depletion layer of 300m.