Certain aspects of the present disclosure provide a bulk acoustic wave (BAW) resonator having a substrate with a heatsink region and an electrical insulator region. An example electroacoustic device generally includes a piezoelectric layer, a first electrode structure, a second electrode structure, one or more reflector layers, and a substrate having a heatsink region and an electrical insulator region. The heatsink region is arranged under a first portion of the first electrode structure, the first portion of the first electrode structure overlapping the second electrode structure. The insulator region is arranged under a second portion of the first electrode structure, the second portion of the first electrode structure being adjacent to the first portion of the first electrode structure.