The present disclosure relates to a transistor device having a germanium cap layer that is able to provide for a low interface trap density, while meeting effective oxide thickness scaling requirements, and a related method of fabrication. In some embodiments, the disclosed transistor device has a channel layer disposed within a semiconductor body at a location between a source region and a drain region. A germanium cap layer is disposed onto the channel layer. A gate dielectric layer is separated from the channel layer by the germanium cap layer, and a gate region is disposed above the gate dielectric layer. Separating the gate dielectric layer from the channel layer allows for the germanium cap layer to prevent diffusion of atoms from the channel layer into the gate dielectric layer, thereby provide for a low interface trap density.