We aimed to develop a high power rectifier of 2.45 GHz with a GaN schottky diode that had 107 V of the breakdown voltage. We used an unpackaged diode with submount to make heat radiation characteristics better. In simulations, the RF-DC conversion efficiency of 71.3% was achieved at 20 W of the input power. In experiments, the RF-DC conversion efficiency of 40.1% was achieved at 20 W of the input power. In the future, we are going to explicit the cause of the difference between simulations and experiments, and try to increase the efficiency.