RF components dealing with high frequency signals are most important in wireless communication system and the performance of the system depends on them. In order to realize highly miniaturized and fully integrated MMICs, the development of miniaturized on-chip passive components is indispensable. The development of miniaturized on-chip passive components with low port impedances will especially greatly reduce the size of MMICs by removing bulky impedance transformation circuits between the passive components and low-impedance FETs generally, the input and output impedances of the FETs are much lower than 50 Ω in the RF frequency. Therefore, impedance transformation circuits should be employed for impedance matching between 50 Ω - based passive components and low-impedance FETs [1-5]. However, in case of fabricating low impedance line using the conventional microstrip with ground metal on the backside of GaAs substrate, the width of the line becomes very large. For instance, when making 15 Ω line on the GaAs substrate with 100 Ωm height, the width of the line reaches 800 Ωm.