The crystal struct.ure of thermally oxidized Ge was invcst.igated by high-resolution electron microscopy (HREM), mainly the interfacc Ge/oxide. Under special conditions tho readion Ge + 0, + GeO, which takes place at (111) surface planes leads t o suitable t)hin crystal regions. The GeO, occurs normally as amorphous films on the crystal surface.Furthernlore, hexagonal GeO, can grow at the interface Ge/oxide by a topotaxial reaction ; t,he orientation relation between these two lattices was ascertained. Intensive electron irradiation was used t o initiate and to observe structure changes in boundary regions.Die Kristallstrukt.ur von therrnisch oxidierteii Ge Kristallen wurde iiiit Hilfe der HochauflSsungsmikroskopie (HREM) untersucht, hauptsiichlich die Grenzfliiche Ge/Oxid.