We present a novel on-chip method for quantitative two-dimensional differential phase imaging. This technique uses four circular holes (600 nm diameter, 1.2 μm spacing) arranged in a "plus" pattern that are fabricated in a layer of metal above a complementary metal-oxide semiconductor (CMOS) imaging sensor. The interference pattern of the aperture shifts position with respect to the differential phase of the incident light. By imaging the interference pattern with the CMOS sensor, this method measures amplitude and differential phase (1°/μm sensitivity for signal-to-noise ratio ≥16 dB) of the incident light field simultaneously. An application to optical beam profiling is presented; we show the amplitude and differential phase profiles of a Gaussian laser beam and an optical vortex.