In the terahertz band, diode size can no longer be ignored compared with the wavelength, significant parasitic parameters will be introduced due to diode package. So it is very necessary to establish three-dimensional model to extract parasitic parameters. Meanwhile manual assembly becomes more difficult, circuit uncertainty will increase. Based on planar Schottky barrier diode designed by China Electronics Technology Group Corporation-13(CETC-13) and University of Electronic Science and Technology of China(UESTC) fabricated on 12 μm thick suspended GaAs substrate a 330 GHz GaAs monolithic integrated sub-harmonic mixer is presented. Test results show that the minimum conversion loss is 10.4 dB at 328 GHz. SSB conversion loss is less than 14.7 dB from 320~340 GHz when the LO power is 5 mW.