Thermoelectric effects on phase change memory elements are computationally analyzed through 2-D rotationally symmetric finite-element simulations of reset operation on a Ge2Sb2Te5 (GST) mushroom cell with 10-nm critical dimension. Temperature-dependent material parameters are used to determine the thermoelectric contributions at the junctions (Peltier heat) and within GST (Thomson heat). Thermal boundary resistances at the GST interfaces enhance the Peltier heat contribution. Peak current densities and thermal gradients are in the order of 250 MA/cm(2) and 50 K/nm. Overall, thermoelectric effects are shown to introduce significant voltage polarity dependence on the operation dynamics, peak temperatures, thermal gradients, volume of the molten region, energy required, and resistance contrast. Resistance contrasts of similar to 8.8 x 10(3) were realized with 155 mu A for the positive polarity and 245 mu A for the negative polarity.