The present invention is a temperature stable integrated optical device which is substantially insensitive to temperature variations. The device, such as an interferometer, includes sub-sections of a different light transmissive material within the optical pathways. The relative lengths of the two different material waveguides can be selected so as to achieve temperature insensitivity. A suitable balance is to ensure that the ratio of the difference in sub-path lengths of the first and second materials is equal to the ratio of the refractive index gradient with temperature of the second material to the refractive index gradient with temperature of the first material. Preferable materials are silicon and silicon nitride.