Annealing effect on net acceptor concentration in ZnSe:N is investigated. ZnSe:N homo-epitaxial layer was grown at 823 K by MOCVD using ammonia (NH3) as a dopant source. Photoluminescence (PL) spectra measured on as-grown layer exhibited the strong deep donor-acceptor pair (D(d)AP) emission and the weak I-l(N) emission line. In order to enhance the activation of nitrogen in ZnSe epitaxial layer, sample was annealed at the 823 K in nitrogen (N-2) and hydrogen (H-2) atmosphere. Only the annealing in nitrogen atmosphere increased IN emission intensity indicate the activation of nitrogen acceptor. And net acceptor concentration was estimated to be 3 x 10(17) cm(-3) by C-V measurements. This activation mechanism is interpreted as hydrogen is released from N-H bonds during annealing in nitrogen atmosphere. (C) 2004 Elsevier B.V. All rights reserved.