We experimentally demonstrate a high-quality phase shift keying demodulator based on a silicon photonic wire waveguide. Since the birefringence of the waveguide generates extremely huge differential group delay, an ultra-compact and high-extinction-ratio delay line interferometer is devised in TE and TM modes. We firstly calculated and simulated the requirements for propagation length and waveguide's dimensions. Then, we measured the interference spectrum, eye pattern, bit error rate, and temperature dependence to ascertain its feasibility for DPSK demodulation. For a 2.8 cm-long wire waveguide, a free spectral range of 9.6 GHz and an error-free DPSK demodulation around 10 Gb/s are obtained.