The RTD device of the present invention is comprised of a semiconductor substrate and a substantially thin conductive metal layer disposed upon the semiconductor substrate, wherein the conductive metal has a substantially linear temperature-resistance relationship. The conductive layer is etched into a convoluted RTD pattern, which consequently increases the overall resistance and minimizes the overall mass of the RTD assembly. A contact glass cover and a conductive metal-glass frit are placed over the RTD assembly to hermetically seal the RTD. The resultant structure can be “upside-down” mounted onto a header or a flat shim so that the bottom surface of the semiconductor substrate is exposed to the external environment, thus shielding the RTD from external forces. The resultant structure is a low mass, highly conductive, leadless, and hermetically sealed RTD that accurately measures the temperature of liquids and gases and maintains fast response time in high temperatures and harsh environments.