A novel rib waveguide-integrated switch is proposed and theoretically discussed. The device is based on the total internal reflection phenomenon (TIR) and the thermo-optic effect (TOE) in hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si). It takes advantage of a bandgap-engineered a-Si:H layer to explore the properties of an optical interface between materials showing similar refractive indexes but different thermo-optic coefficients. In particular, thanks to modern plasma-enhanced chemical vapor deposition techniques, the refractive index of the amorphous film can be properly tailored to match that of c-Si at a given temperature. TIR may be achieved, however, at the interface by acting on the temperature, because the two materials have different thermo-optic coefficients. The switch is integrated in a 4-μm-wide and 3-μm-thick single-mode rib waveguide. The substrate is a silicon-on-insulator (SOI) wafer with an oxide thickness of 500 nm. The active middle region optimal length is 282 μm. The device performance is analyzed at a wavelength of 1.55 μm. It is shown that the output crosstalk and insertion loss are less than −26 and 3.5 dB, respectively. © 2003 Society of Photo-Optical Instrumentation Engineers.