Microelectronic thermoelectric generators (TEGs), which can recycle waste heat into electrical power, have applications ranging from the on-chip thermal management of integrated circuits to environmental energy sources for Internet-of-things sensors. However, the incompatibility of TEGs with silicon integrated circuit technology has prevented their broad adoption in microelectronics. Here, we report TEGs created using nanostructured silicon thermopiles fabricated on an industrial silicon complementary metal–oxide–semiconductor (CMOS) process line. These TEGs exhibit a high specific power generation capacity (up to 29 μW cm−2 K−2) near room temperature, which is competitive with typical (Bi,Sb) 2 (Se,Te) 3 -based TEGs. The high power capacity results from the ability of CMOS processing to fabricate a very high areal density of thermocouples with low packing fraction and to carefully control electrical and thermal impedances. TEG power was also found to increase significantly when thermocouple width was decreased, providing a path to further improvements. Unlike (Bi,Sb) 2 (Se,Te) 3 TEGs, our silicon integrated circuit TEGs could be seamlessly integrated into large-scale silicon CMOS microelectronic circuits at very low marginal cost.