A nanophononic metamaterial-based thermoelectric energy conversion device and processes for fabricating a nanophononic metamaterial-based thermoelectric energy conversion device is provided. In one implementation, for example, a nanophononic metamaterial-based thermoelectric energy conversion device includes a first conductive pad, a second conductive pad, and a plurality of strip units. In one implementation, the first conductive pad is coupled to a first connection of the thermoelectric energy conversion device, and the second conductive pad is coupled to a second connection of the thermoelectric energy conversion device. The plurality of strip units are connected in series between the first and second conductive pads and provide a parallel heat transfer pathway. The strip units include a nanostructure design comprising a nanophononic metamaterial.