An ultracompact and broadband silicon wavelength demultiplexer based on SWG-assisted directional coupler is designed and experimentally demonstrated for wavelength splitting of 1310 and 1550 nm. The embedded SWG enables significantly reduced footprint, due to the precise phase matching at 1550 nm and large phase mismatch at 1310 nm. As a result, the fabricated device has a length of only 9 μm, and provides high extinction ratios (ERs) of 23 dB and 19 dB at 1310 and 1550 nm, respectively. Its 3-dB bandwidths are 85 nm for O-band (ER > 15 dB) and 140 nm for C-band (ER > 10 dB).