This paper describes a new process technique for batch process of SOI(Si-on-Insulator) structures with buried cavities for MEMS(Micro Electro Mechanical System) applications by SDB(Si-wafer Direct Bonding) technology and electrochemical etch-stop. A low-cast electrochemical etch-stop method is used to control accurately the thikness of SOI. The cavities were made on the upper handling wafer by Si anisotropic etching. Two wafers are with an intermediate insulating oxide layer. After high-temperature annealing(1000℃, 60 min.), the SDB SOI structure with buried cavities was thinned by electrochemical etch-stop. The surface of the fabricated SDB SOI structure have more roughness that of lapping and polishing by mechanical method. This SDB SOI structure with buried cavities will provide a powerful and versatile substrate for novel microsensors and microactuators.