Using analysis and numerical simulation, we have investigated near-infrared and mid-infrared second-harmonic generation (SHG) and sum frequency generation (SFG) in crystal silicon (SOI) waveguides that possess a strong second-order nonlinear susceptibility by virtue of a Si(3)N(4) straining layer applied directly to the top surface of the waveguide. This layer induces anisotropic compressive strain in the waveguide core. Using the technique of TE/TM mode birefringence, we have derived waveguide geometries for both slab and strip channel waveguides that offer perfect phase matching of three lightwaves for SHG/SFG along a uniform waveguide, thereby offering the prospect of efficient wavelength conversion in monolithic silicon photonics.