The a-Si: H/a-SiCx: H superlattices were fabricated by r. f. plasma CVD. The blue shift of optical bandgap and construction of the superlattices were present. The interface abruptness was determined by low-angle X-ray diffraction. The constant photocurrent method and IR measurement showed that there existed excess hydrogen and high concentration of Si-C bonds at a-Si:H/a-SiCx:H interfaces. The thermal stability of interfacial hydrogen was poor. The interfacial defect density was about １．２×１０１１ｃｍ-2.