This paper presents a 3D-printed THz hemispherical lens antenna integrated with the open-ended rectangular waveguide at WR-10 band for antenna characteristics enhancement, e.g., gain and half-power beamwidth (HPBW). The digital light processing (DLP) technique, which is one of the famous 3D printing techniques, is chosen for fabricating the hemispherical lens antenna. The proposed design can be integrating the 3D-printed lens antenna without any extra assistant tools during assembly lensantenna with an open-ended WR-10 waveguide. In the simulation, the lens radiuses are investigated by varying from 2 mm to 5 mm in step with 1 mm. The optimum dimensions of the 3D-printed hemispherical lens antennas are obtained by using the 3D electromagnetic simulation tools. Based on the simulation results, at 90 GHz, the lens radiuses of 2 mm, 3 mm, 4 mm, 5 mm, and 6 mm, provide the maximum realized gain of 11.7 dBi, 13.1 dBi, 14.8 dBi, 15.8 dBi, and 16.3 dBi, respectively. The proposed technique gives many advantages, including ease of design, inexpensive material, low-cost fabrication process, rapid prototyping, etc. Moreover, the narrow HPBW and high gain of the proposed lens antenna can be applied to the 6G beamsteering frontend system.