In this work we present the fabrication and characterization of an electro-optical temperature sensor based on silicon oxynitride dielectric films deposited by Plasma Enhanced Chemical Vapor Deposition at low temperatures (∼300°C). The temperature sensor is basically a MachZehnder interferometer such that a temperature difference between its arms produces a phase difference between the electromagnetic waves traveling through each arm thus originating a variation in the output optical power. In order to analyze the feasibility of this sensor, a temperature difference is imposed by applying a heating element in one of the arms. The results show that it is possible to control the optical device output through the adequate control of the heating element. Furthermore, the influence of heat propagation, multimode noise and methods to obtain monomode optical waveguides and self-sustained Mach-Zehnder structures are discussed in this work. © 2006 The Electrochemical Society.