The present invention relates to a method of manufacturing semiconductor device with composite buffer layers. The method includes etching grooves in n type and p type semiconductor wafers respectively. The areas of grooves in n type wafer just correspond to the areas without grooves in p type wafer, and vice versa. The grooves in both n type and p type wafers have the same depth. Two wafers are directly bonded together so that the grooves in one wafer are filled with the grooves in the other wafer. Then, chemical bonding is implemented. The bonding may also be made through thin dielectric layer (e.g. SiO.sub.2). If necessary, grinding, polishing or chemical mechanical polishing processes are carried out to remove the redundant material. Thereby, it is easy to manufacture the semiconductor device with composite buffer layer as voltage sustaining layer.