In the report results of optimization of the planar diodes based on GaAs/AlAs superlattices for use in devices of THz range of frequencies are considered. The purpose of optimization was reduction of value of series resistance of losses Rs and parasitic capacity Cpar of a substrate of the diode. The Rk contains have been designed. It is found, that at the area of active region of the diode less 2times10-8 sm2, the maximal contribution to value of Rs gives resistance of the small area ohmic contact. For its reduction it was used the additional thin (100 nm) high-doped GaInAs contact layer located between ohmic contact and a superlattice. From measurements of full size of Rs for a massive from 100 diodes the value of the specific resistance of ohmic contact with an additional contact layer equal 2times10-7 OM/sm2 is received.