We report the fabrication of GaN/AlGaN nanocolumn LEDs on n‐(111) Si substrates by RF‐MBE for the first time. Clear diode characteristics with a turn‐on voltage of 4 V and an ultraviolet emission spectrum with a peak wavelength of 354 nm were observed at room temperature. When the Al composition of p‐Al_x Ga_1–x N was changed from 8.8% to 25.1%, the high Al content led a narrowing of the FWHM compared withthat for low Al contents due to the suppression of carrier overflow. We measured the electroluminescence (EL) under dc and pulsed operations. The integrated EL intensity under the pulsed operation was 3 times as strong as that under the dc operation at 100 mA due to the reduced generation of heat. The thermal resistance was estimated to be 40 °C/W from the EL peak wavelength difference between the dc and pulsed operations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)