elements used for amplification, be it Josephson junctions or high kinetic inductance materials. Here we report on the development of a fabrication process for vacuum-gap microstrips, a design in which the ground plane is suspended in close proximity above the center conductor without the support of a dielectric. In addition to high-capacitance transmission lines, this architecture also enables air-bridges and compact parallel-plate capacitors. The performance of the fabrication is examined using distributed aluminum and granular aluminum resonators in a cryogenic dilution refrigerator setup, showing quality factors on par with the fabrication processes used in state-of-the-art TWPAs. In addition to characterizing the dependence of the quality factors on power, also their behavior with respect to temperature is explored, applying a model based on thermal quasi-particles and saturable two-level systems (TLS), showing that the quality factors of the resonators are limited by TLS.