This letter presents a design of two compact, light, rigid, and low-cost three-dimensionally (3-D) printed millimeter-wave antennas for a fifth-generation (5G) communication system. The proposed antennas consist of a radiating slot that is surrounded by a rectangular cavity and corrugations, which boost the gain performance of the antennas. Furthermore, the proposed antennas are fabricated using 3-D printing technology, and they are metalized using novel, simple, and low-cost techniques, which utilize the commercial conducive spray-coating technology. The proposed antennas operate at a 28 GHz band, where the first design is fed by a waveguide to prove the performance, whereas the second design is fed by a microstrip line to demonstrate the ability to be integrated into a compact structure. Measurement results show a wide impedance bandwidth, which enables the proposed antenna design to be a strong candidate for 5G applications.