In this paper, effective dielectric constant, line attenuation and characteristic impedance, average power handling capability (APHC) of DC-biased thin film microstrip line (TFML) as interconnection for monolithic microwave integrated circuits (MMICs) is investigated. The TFML is fabricated on standard low resistivity silicon (LRS) substrate (rho les 10 Omega-cm ) by incorporating a spin-on dielectric polyimide and sputtering of aluminum. An accurate on-wafer-procedure for extracting the microwave characteristics of TFML up to 50 GHz is described and the method is successfully applied to low-K polyimide deposited on the silicon.