This study presents an innovative method for in situ measurements of electrical conductivity at microwave frequencies using a dielectric resonator (DR)-based probe. The DR, excited in the transverse electric mode with azimuthal index 0, radial index 1, and an open (non-integer) axial field variation denoted by δ (TE01δ mode) by a ridged waveguide, interacts with metallic layers as small as 5 × 5 mm2 on a dielectric substrate, enabling precise conductivity measurements through reflection coefficient analysis and electromagnetic simulations. Validation is performed by comparing the probe’s conductivity extraction results at 13.28 GHz with a conventional resonant cavity method at 10 GHz, demonstrating strong agreement. The used samples are therefore much smaller than what other comparable methods would require. The method is further applied to additively manufactured metallic deposits produced via a micro-dispensing technique, providing insights into their high-frequency (HF) conductivity and the effects of surface roughness. Additionally, a second-generation contact-based probe is developed to extend the characterization capabilities to larger samples and perform HF surface conductivity mapping. This advancement enables localized evaluations of surface properties and correlations with roughness, offering a valuable tool for optimizing additively manufactured components for HF applications.