Sub-Terahertz 303 GHz rectenna was developed by the photolithography process and measured using a 300 kW-class Gyrotron. As a result, the maximum output power and rectenna power density for the microstrip line (MSL) and coplanar waveguide (CPW) were 17.1 mW, 3.43 kW/m 2 , and 14.5 mW, 4.87 kW/m 2 , respectively. The RF-DC conversion efficiency was obtained 2.17 % with 342 mW input power and 130 $\Omega$ DC load. The results reveal the highest operation frequency except the photovoltaic converter.