A device and techniques for fabricating the device are described for forming a wafer-level thermal sensor package using microelectromechanical system (MEMS) processes. In one or more implementations, a wafer level thermal sensor package includes a thermopile stack, which includes a substrate, a dielectric membrane, a first thermoelectric layer, a first interlayer dielectric, a second thermoelectric layer, a second interlayer dielectric, a metal connection assembly, a passivation layer, where the passivation layer includes at least one of a trench or a hole, and where the substrate includes a cavity adjacent to the at least one trench or hole, and a bond pad disposed on the passivation layer and electrically coupled to the metal connection assembly; and a cap wafer assembly coupled to the thermopile stack, the cap wafer assembly including a wafer having a cavity formed on a side of the wafer configured to be adjacent to the thermopile stack.