An optical switch that is constructed on a substrate having first and second waveguides that intersect at a gap having a predetermined width. The first and second waveguides are positioned such that light traversing the first waveguide enters the second waveguide when the gap is filled with a liquid having a first index of refraction. The gap is part of a trench in the substrate having a first region that includes the gap and a second region adjacent to the first region. The second region has a width greater than the width of the first region. A liquid having the first index of refraction is disposed in the first region. The liquid generates a gas when heated to a predetermined temperature. A first heater is disposed in the first region for heating the liquid to the predetermined temperature thereby generating a gas bubble in the liquid at the gap. Light traversing the first waveguide is reflected by the gap when the gap is filled with a gas. To change the switch into the non-reflecting state, the bubble is displaced to the second region of the trench, in response to a control signal. The displacement mechanism can be constructed from a second heater having a portion thereof located in the first region between the first heater and the second region. The displacement mechanism can also be constructed from a mechanism that applies a pressure differential across the first region thereby causing the bubble to partially extend into the second region. A third waveguide having an end terminating on the trench can also be included in the optical switch. The third waveguide is positioned such that light traversing the first waveguide enters the third waveguide when the gap is not filled with liquid.