The use of nonequilibrium annealing approaches can produce very high levels of arsenic electrical activation in Si. However, subsequent thermal treatments between 500 and 800 degrees C easily deactivate the dopant to a level one order of magnitude below the solid solubility. In this work, the authors study the deactivation of laser annealed (LA) ultrashallow arsenic distributions in silicon using Hall effect measurements, extended x-ray absorption fine structure spectroscopy, and secondary ion mass spectrometry. Single crystal Si (100) wafers implanted with As ions at 2 keV energy and different doses were activated with a millisecond LA at 1300 degrees C using a scanning diode laser annealing system under nonmelt conditions. The samples were then thermally treated in a furnace at 300-900 degrees C in a N-2 atmosphere for 10 min. Electrical deactivation has been observed for all the implanted doses but for the lowest one. In particular, it was observed that the higher the As dose the easier the deactivation, in particular, after the 700 degrees C post-LA treatment. At 900 degrees C, in-depth diffusion and a resulting reactivation has been observed for samples implanted with 1x10(15) and 3x10(15) cm(-2).