Surface defects on two types HD SIMOX wafers that made of CZ wafers and epitaxial wafers as starting materials were examined for their shape and density. It was found that surface defects on HD SIMOX wafers were mainly classified into two categories. One was "pit-type" and another was "undulation-type". It is considered that the former defects are originated from grown-in defects, such as COPs, and the latter defects are caused by SIMOX process, such as oxygen ion implantation and/or SIMOX anneal. Furthermore, deformations of surface defects by sacrificed oxidization for SOI thinning and the influences on GOI and BOX quality were investigated. It was found that some undulation-type defects that lost the SOI layers during SOI thinning degraded GOI and that some other undulation-type defects that lost aboriginally the SOI layers degraded both the GOI and BOX quality.