We developed GaN schottky barrier diode (SBD) for sub-terahertz rectenna to improve the RF-DC conversion efficiency and DC output power. Designed a GaN SBD using the device simulator and fabricated prototype. The similar 1-V curve was obtained between measurement and simulation. Furthermore, calculated the theoretical RF-DC conversion efficiency on the rectenna. As a result, diodes with series resistance 3.6 Ω, junction capacitance 0.035 pF and breakdown voltage 46.3 V were calculated. The RF-DC conversion efficiency of 78% was theoretically obtained at 303 GHz. This work showed RF-DC conversion efficiency can be greatly improved using GaN SBD for rectenna in sub-terahertz (herein 100 GHz ~ 700 GHz).