We demonstrated an arrayed-waveguide-grating (AWG) demultiplexer using Si photonic wire waveguides, for the first time. We designed and fabricated an AWG of 110 ×93 µm 2 size on a silicon-on-insulator substrate. The demultiplexing function was observed in the wavelength range of 1.50–1.57 µm with a channel spacing of ∼6 nm and a free spectral range of > 90 nm. A narrower channel spacing of 1 nm is possible in an area of ∼(500 µm) 2 , using an optimization of arrayed waveguides and slab waveguides.