Abstract: The thermal treatment is one of the main processes for the production ofdetector-grade (DG) silicon by neutron transmutation doping (NTD), it is requi-red to maintain and to enhance minority carrier lifetime of the silicon crystalduring the treatment. In this work annealling of DG-NTD Si is performed indiffusion furnaces under controlled temperature and with HCl added into theprotective atmosphere, After annealling the minority carrier lifetime is over 1000μs,the homogeneity of the resistivity is good.