In this letter, stacked sidewall-damascene double-layer poly-silicon trigate field effect transistors (FETs) with and without rapid thermal annealing (RTA) are successfully demonstrated using a simple fabrication method. Devices with RTA exhibit superior electrical characteristics to those without RTA owing to better crystallinity. The better crystallinity of the device with RTA results from a larger grain size and fewer defects, leading to higher field-effect mobility compared with devices without RTA. p-type stacked sidewall-damascene double-layer poly-Si trigate FETs with RTA show excellent electrical characteristics, including an extremely low drain-induced barrier lowering (DIBL) of 7 mV/V, a steep subthreshold swing of 136 mV/decade, and high current ratio of. The fabricated n-type stacked sidewall-damascene double-layer poly-Si trigate FETs with RTA showed a low DIBL, subthreshold swing and an current ratio larger than seven orders of magnitude. Their simple fabrication method makes them a promising candidate for future monolithic 3D integrated-circuit applications.