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We propose a scalable RF subcircuit FET model using BSIM3v3 by adding one of BSIM4's Intrinsic Input Resistance (IIR) models (rgateMod=3) for S11 scalability as well as a simple RC substrate network with well defined intrinsic FET's parasitic estimation including partitioned junction diodes for S22 scalability. Using this simple model, we could achieve a reasonable scalability with variations of L, W, VGS, and VDS for S11 up to 25 GHz. We also suggest new S-parameter test structure for FETs with Ring Substrate Contact (RSC). This new layout scheme allows for improved S22 scalability up to about 10 GHz; as well as reduces the punch through effect in DC I-V characteristic of large width NFETs. In addition, comparing to NFETs without RSC, we also report substantial Rsub lowering, FT and NFmin worsening, and Csub influence on S22 contours for NFETs with RSC in detail.