A new method is is developed for accurate extraction of the effective mobility (μeff) in the multifinger nMOSFETs with various poly-to-poly (PO-PO) spaces. The wide PO-PO space intends to increase the tensile stress from a contact etching stop layer (CESL) and yields higher μeff in the nMOSFETs. However, the source resistance (RS) emerges as a critical parasitic element in the multifinger devices with a large finger number. The wide PO-PO space generally leads to the further increase of RS, which may offset μeff improvement and degrade transconductance (gm). A two-end source line is proposed to reduce RS and the impact on gm. The complicated layout-dependent effects containing the CESL strain, RS, and 3-D fringing capacitances bring a crucial challenge to the μeff extraction. In this paper, a distributed transmission line model is derived for a reliable determination of RS, which is a key to the realization of accurate extraction of μeff and layout-dependent effects in multifinger devices.