Oxygen-18 substituted strontium titanate is developed as a capacitive thermometer at cryogenic temperatures under intensive magnetic fields. Conventional resistive thermometers used for cryogenic thermometry vary by up to a few percent under high magnetic fields, causing them to have to be extensively calibrated for such conditions.[1] On the other hand, strontium titanate (SrTiO₃) has shown to be an effective capacitive thermometer that is fairly stable under similar magnetic fields, varying only by a few hundreths of a percent. This has been utilized to measure the thermal Hall effect in Bismuth down to 40 K.[2] However, the sensitivity of SrTiO₃ thermometers drops to zero under 7 K, rendering them unusable for measurements in the milliKelvin range. The capacitance behaviour of strontium titanate changes when oxygen-16 is substituted for oxygen-18, specifically moving the low sensitivity region to higher temperatures.[3] Thus we explore the possibility of using oxygen-18 substituted SrTiO₃ as a capacitive thermometer in the milliKelvin range at high magnetic fields, with the aim to utilize them for thermal transport measurements in Kondo insulator YbB₁₂.