In this work, Ge-based high-hole-mobility transistor with Si compatibility is designed, and its performance is evaluated. A 2-dimensional hole gas is effectively constructed by a AlGaAs/Ge/Si heterojunction with a sufficiently large valence band offset. Moreover, an intrinsic Ge channel is exploited so that high hole mobility is preserved without dopant scattering. Effects of design parameters such as gate length, Ge channel thickness, and aluminum fraction in the barrier material on device characteristics are thoroughly investigated through device simulations. A high on-current above 30 μA/μm along with a low subthreshold swing was obtained from an optimized planar device for low-power applications.