Excitations of surface plasmon polaritons at metal/dielectric interfaces can lead to a number of interesting optical effects in nonlinear harmonics generation, nanofocusing, enhanced optical scattering and emission. In particular, Raman signals from molecules in contact with or close proximity of metallic nanostructures can be enhanced by many orders of magnitudes, a phenomenon called surface-enhanced Raman scattering (SERS). Studies have shown that with certain plasmonic nanostructures, the SERS signals are detectable even in single molecular level, making SERS a potential label-free and high-sensitivity bio/chemical sensing modality. However, it is challenging to reach single molecule SERS in a reproducible way, as nanogaps between plasmonic nanostructures are commonly required. While nanopatterning techniques such as electron beam lithography are versatile in creating various nanostructures, creating nanogaps below 20nm reducibly remains a challenge. Here we present plasmonic patch antennas as a platform for SERS applications. The patch antennas are made of metallic patches on the top of a metal film separated by a dielectric layer. This vertical metal-dielectric-metal design makes it possible to reproducibly control the gap size in nanometers by using thin film deposition techniques such as atomic layer deposition. In this talk, we will present numerical and experimental studies on resonant cavity modes of these plasmonic patch antennas, a simple expression relating the cavity resonant frequencies with the geometric parameters of the antennas. We will also present experimental tests on SERS enhancement factors by the plasmonic patch antennas, and a comparison of their performances with commercial SERS substrates.