A novel symmetric layout structure is proposed for a switchable differential inductor (SWD-inductor). The proposed structure overcomes the problem of quality factor degradation encountered when using SWD-inductors in the traditional quadrangular spiral layout. On the basis of the substrate loss density distribution predicted by an electromagnetic (EM) wave simulator, the reason for the quality factor improvement in our proposed novel SWD-inductor structure is interpreted. Two testkeys with the novel and the traditional layout structures are fabricated using 0.18-μm RF CMOS technology. Under identical criterion of area consumption and inductance values for the testkeys, the experimental data show that our proposed structure improves the quality factor by 41% at 1.8 GHz when the switch is turned off and by 24% at 7.5 GHz when the switch is turned on.