This paper discusses the engineering of ultra-shallow junctions for advanced semiconductors using an annealing technique called Flash-Assist RTP TM (fRTP). This technique offers effective process times in 1–10 ms. A discussion on the evolution of rapid thermal processing (RTP) based on the thermal response time of the heat source and wafer is presented. Technical innovations required for fRTP are discussed including why an extremely powerful flash lamp is essential for this application. It is shown that a process engineer can more or less independently control diffusion and activation over a wide range, enabling the formation of junctions meeting future requirements of semiconductor manufactures.