An aluminum-wire grid polarizer fabricated directly on a gallium–arsenide photodiode is used to realize a polarization-selective photodetector. Since all of the light transmitted through the wire grid, including higher-order diffraction components, can be detected at the photodiode and since a resonance of incident electromagnetic waves is utilized, the required grid period can be significantly larger. With a grid period of 600 nm and normal incident light at 715 nm, an extinction ratio of 16 can be obtained both for light detected at the photodiode and light reflected from the surface. If light detected at the photodiode is to be optimized, a higher extinction ratio of 30 and a loss of 30&percent; have been experimentally obtained as well. These experimental results are in good agreement with our theoretical simulation. ©1997 American Institute of Physics.