According to some embodiments, low-temperature (cryogenic) nuclear magnetic resonance (NMR) probe fixed capacitors include thermally-conductive dielectric layers serving to thermally connect the capacitors to a cryogenic heat sink. For example, a sapphire layer may be metalized on opposite sides to form copper capacitor plates, and along an edge to form a copper heat sink contact. Heat generated by RF currents during an operation of an NMR circuit including such a capacitor is discharged through the thermally-conductive dielectric to the heat sink. Cooling cold-probe circuit components such as capacitors through thermally-conductive capacitor dielectrics allows reducing perturbations introduced into the circuit by components such as heat sinks.