Effective pregate surface passivation and postgate treatments are very important to optimize the germanium metal-oxide-semiconductor (MOS) interface quality. In this work, pregate GeO2 surface passivation and postgate treatments including CF4-plasma treatment and forming gas annealing are employed to make high quality HfO2 gated germanium MOS capacitors. Excellent electrical characteristics with negligible capacitance-voltage stretch-out and frequency dispersion are achieved. The interface trap density of TaN/HfO2/GeOx/Ge MOS structure is as low as 2.02×1011 cm-2 eV-1 at the minimum. Comparing to the forming gas annealing, it is found that CF4-plasma treatment is more effective to passivate interface states located in the upper half of Ge bandgap.