We use atomistic simulations to study the electrical double layer (EDL) at an electrode–electrolyte interface at different temperatures. For a constrained electrode charge, the potential drop over the EDL increases with temperature, a phenomenon known as the thermal voltage rise (TVR). Prior continuum models attributed TVR to expansion of the EDL with increasing temperature; conversely, our simulations with aqueous, organic, and ionic liquids show that the EDL does not expand but that the TVR is caused by a decrease in interfacial permittivity with increasing temperatures.