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Precise determination of transistor electrical parameters is essential for accurate circuit simulation. The strong geometric dependences of MOS transistor electrical parameters can be modeled by the inverse-geometry formula. However, special care is needed in using the inverse-geometry formula. To prevent the short-channel and narrow-width effects being adversely mirrored to the drain-current evaluation of large transistors, we propose to clamp the dependences of transistor electrical parameters on small-geometry effects at a boundary (L CLP, W CLP). In principle three transistors with two different channel lengths and two different channel widths are required to extract the geometric dependence of various electric parameters. Our analysis shows that a set of five test transistors can increase the extraction accuracy by a factor of two, and thus is a better choice when both the modeling accuracy and test clip complexity are considered.