Electrothermal couplings between supply voltage, operating frequency, power dissipation and die temperature have been shown to significantly impact the energy-delay-product (EDP) based simultaneous optimization of supply (Vdd) and threshold (Vth) voltages. We present for the first time, the implications of an electrothermally aware EDP optimization on circuit operation in leakage dominant nanometer scale CMOS technologies. It is demonstrated that electrothermal EDP (EEDP) optimization restricts the operation of the circuit to a certain region in the VddVth plane. Also, the significance of EEDP optimization has been shown to increase with increase in leakage power and/or process variations. Categories and Subject Descriptors B.7.1 [Hardware]: Integrated circuits ? VLSI. General Terms Performance, Design. Keywords Electrothermal couplings, energy delay product, subthreshold leakage, temperature aware design.