A silicon rib waveguide that has a silicon nitride cladding layer of predetermined thickness to reduce optical loss of light propagating therethrough. An exemplary embodiment of the waveguide is fabricated by using a silicon-on-insulator structure having a single crystal silicon layer bonded to a silicon wafer with a layer of insulative material. An etch resistant masking layer is deposited on the outer surface of the single crystal silicon layer and patterned to produce vias therein. A RIE etching process is used through the vias in the masking layer to form at least one rib bounded by a pair of parallel trenches. The masking layer is removed and a silicon nitride cladding layer is deposited on the rib side and end walls and on the trenches.