The effects of CW CO2-laser irradiation on semiconductors are studied with primary emphasis on the physics of the process. Experimental results and theoretical considerations show that semiconductor sample can be heated to desired temperatures by CW CO2-laser irradiation. The CW CO2-laser irradiation with wavelength of 10.6 μm is different from the other short wavelength lasers in the following features: light absorption of laser radiation through free carrier absorption, uniform temperature distribution throughout the thickness of the wafer, enhancement of annealing efficiency by laser irradiation from back surface. The temperature profile produced by stationary CW CO2-laser irradiation is capable of annealing As+ ion implantation damage in Si with a solid-state regrowth mechanism. During the regrowth process the implanted As+ ions are incorporated into substitutional lattice sites and can be made electrically active to a high degree without redistribution of the original profile. Using CO2-laser irradiation from the back surface we have produced ohmic contacts with excellent electrical properties for GaAsFET without damaging the device structure on the front surface.