We present a compact silicon polarization rotator (PR) based on mode-hybridization by breaking the cross-sectional symmetry of a double-stair waveguide. The device fabrication is fully compatible with the commonly used silicon photonics processes with no extra masks required. The dependence of device performance on the double-stair waveguide dimensions is investigated using FDTD simulations. Characterizations of the fabricated devices reveal that the 23-μm-long PR exhibits a polarization extinction ratio (PER) of >17 dB in the wavelength range of 1500-1540 nm. The maximum PER exceeds 30 dB at 1518 nm.