Radical cation salts of TMET-TTP (2-(4',5'-bis(thiomethyl)-1',3'-dithiol-2'-ylidene)-5-(4'',5''-ethylenedithio-1'',3''-dithiol-2''-ylidene)-1,3,4,6-tetrathiapentalene) with various anions show high electrical conductivity. Many of them have a similar structure with two-dimensional donor arrangement.