Paramagnetic metal complexes with tetrathiafulvalene moieties in its ligands, [Cu-II(EDT-sae-TTF)(2)] (1) and two new derivatives were investigated towards the potential application to the organic thin film transistor (OTFT) with magnetic field responsiveness. The complex 1 and its benzene substituted derivative, [Cu-II(Bz-sae-TTF)(2)] (2), gave semiconducting radical cation salts with fairly good electrical conductivity. A field effect transistor (FET) device fabricated with the spin-coated film of 1 was operative, but its performance was quite low. Atomic force microscopy (AFM) images revealed that the spin-coated film of 1 consists of very small grains with the size of about 10nm, which can be responsible for the low device performance.