Terahertz applications have been extensively studied during the last decade since they allow not only increasing the bandwidth of telecom systems but also the detection of many organic molecules in solid and liquid phase, including hazardous materials such as explosives. In this contribution, we present a device that allows generating frequencies in the Terahertz domain through the heterodyning of signals emitted by two distributed feedback lasers made by ion exchange on a erbium-ytterbium co-doped glass. Thanks to the intrinsic thermal stability of the glass substrate, the slow dynamic of the amplifier medium and since the laser pairs are integrated on a single chip and identically pumped by the same sources, stable frequencies have been generated in the millimeter and sub-Terahertz frequency range, without any thermal or electrical control loop being implemented.