This work presents an analytical methodology to estimate the equivalent rectangular aspect ratio of the active region of a Split-Drain MAGFET (SD-MAGFET) by combining known active regions. With this result, a SPICE Macro Model (SMM) for SD-MAGFETs is proposed associating each drain to a MOSFET. The effect of the magnetic flux density is introduced through the substrate-source voltage of each MOSFET, in opposite sense from each other, establishing different channel concentration. The total DC drain current of the equivalent rectangular MOSFET obtained in HSPICE has an error <15% with respect to results experimenttally measured for SD-MAGFETs of W=10μm and different L (2μm, 5μm and 15μm). The drain current imbalance obtained in HSPICE using the proposed SMM has an error <1,6% with respect to results experimentally measured with a SD-MAGFET of W/L=10μm/2μm. ©The Electrochemical Society.