Structures and methods for reducing the thermal resistance of quantum cascade laser (QCL) devices and QCL-based photonic integrated circuits (QCL-PIC) are provided. In various embodiments, the native substrate of QCL and QCL-PIC devices is replaced with a foreign substrate that has very high thermal conductivity, for example, using wafer bonding methods. In some examples, wafer bonding of processed, semi-processed, or unprocessed QCL and QCL-PIC epilayers or devices on their native substrate to a high-thermal-conductivity substrate is performed, followed by removal of the native substrate via selective etching, and performing additional device processing if necessary. Thereafter, in some embodiments, cleaving or dicing individual devices from the bonded wafers may be performed, for example, for mounting onto heat sinks.