In this work, we demonstrate a very high‐energy density and high‐temperature stability capacitor based on SrTiO 3 ‐substituted BiFeO 3 thin films. An energy density of 18.6 J/cm 3 at 972 kV/cm is reported. The temperature coefficient of capacitance ( TCC ) was below 11% from room temperature up to 200°C. These results are of practical importance, because it puts forward a promising novel and environmentally friendly, lead‐free material, for high‐temperature applications in power electronics up to 200°C. Applications include capacitors for low carbon vehicles, renewable energy technologies, integrated circuits, and for the high‐temperature aerospace sector.