In this paper we present a micromachined Thermal Conductivity Detector (TCD), based on the Ultra Low Power (ULP) technology. The device has been electrically characterized with different Helium gas flows, via a microfluidic experimental setup. Extraction of global thermo-electric parameters, exploited for the development of an electro-thermal Spice model, has been performed directly from the experimental measurements and from 3-D electro-thermal FEM simulations of the device. The resulting Spice model agrees very well with the measurements, with a maximum error less than 0.22%.