© 2019 Author(s). Nanocolumn light-emitting diodes (LEDs) are expected to achieve the monolithic integration of the three primary-color micro-LEDs for micro-LED displays. From the viewpoints of low cost and large-area substrates, a technology for the regular arrangement of nanocolumns on Si substrates is required. The improvement of GaN nanocolumns on Si would be an important advance for the preparation of high efficiency optical devices. In this paper, the effects of column diameter and height on the photoluminescence (PL) and cathodoluminescence properties of GaN nanocolumn arrays were investigated. The PL intensity of the 700-nm high (tall) nanocolumn was three times stronger than that of the 350-nm high (short) nanocolumn. Although the PL intensity decreased dramatically with an increasing diameter for the shorter nanocolumns, it retained its high value (up to 220 nm) for the taller GaN nanocolumns. For the latter specimens, a decrease in the number of emitting nanocolumns, which would reduce emission efficiency, was suppressed by the dislocation filtering effect. Moreover, yellow luminescence was suppressed for taller nanocolumns. In the low-temperature-PL spectra, the peak observed at 3.41 eV, related to a stacking fault, increased with diameter regardless of height. These results indicate that the appropriate design of column height and diameter is of considerable importance for obtaining high efficiency emissions. Finally, InGaN/GaN quantum wells were fabricated on the regularly arranged GaN nanocolumn platform. Blue, green, and red (RGB) emission colors with no significant change in emission intensity were observed. These results constitute an important step toward the monolithic integration of RGB micro-LEDs.