Efficiency droop remains a significant problem to be overcome if the performance of LEDs for solid state lighting is to be improved. As more cost effective substrates such as silicon wafers are used on which to grow the LED active layers, the overall output efficiency and efficiency droop at high drive currents need to be monitored and better understood. This paper investigates the droop effect at elevated temperatures for an LED grown on silicon, compared with an LED grown on the more standard sapphire substrate. While the overall output efficiency decreases with increasing temperature, the efficiency droop is found to be relatively independent of temperature.