Gated anode diodes (GADs) composed of high electron mobility transistors with two-step height p-GaN gates were investigated for energy harvesting. The p-GaN gate was designed for low turn-on voltage with thickness of the p-GaN gate region 1 (p-GaN1) and for high breakdown voltage with thickness and length of the region 2 (p-GaN2). The GAD showed 0.2 V turn-on voltage and more than 250 mA/mm at 5 V with 40 nm thick p-GaN1 and 20 nm thick and 4 µm long p-GaN2. The p-n diode with the same structure of the GAD showed 450 V breakdown voltage.