Organic light-emitting diodes (OLEDs) of metal-semiconductor-metal (MSM) structure have been fabricated by using m-MTDATA [4,4',4''-tris (3-methylphenylphenylamino) triphenylamine] as a hole-injection layer (HIL). The m-MTDATA is shown to be an effective hole-injecting material for the OLED, in that the insertion of m-MTDATA greatly reduces the roughness of anode surface, lowers the turn-on voltage, and increases the luminous efficiency. Red, green and blue OLEDs were fabricated, and their color coordinates in CIE chromaticity were found to be (0.600, 0.389), (0.240, 0.525) and (0.171, 0.171), respectively. The luminous efficiencies of the fabricated OLEDs were 1.4 lm/W at 106 cd/m2 for red, 1.4 lm/W at 100 cd/m2 for green, and 2.0 lm/W at 104 cd/m2 for blue.