The performance of CMOS devices improves due to the addition of Ge in their poly-Si gate material. The presence of Ge in the gate increases the current drive due to the reduction of the flatband voltage. The change in the flatband voltage is due to a shift in the valence-band energy level in the gate. This shift results in a change in the barrier height for electrons tunneling from the gate. Thus, the presence of Ge in the gate increases the tunneling current in the gate. This increase may result in a limitation in the use of SiGe gates in future generations of MOSFETs with ultrathin gate dielectrics. The purpose of this work is to investigate the effect of Ge content on the tunneling current in CMOS devices with ultrathin gate dielectrics. © 1999 Materials Research Society.