A derivation of the interband tunneling transmission coefficient is given based on analytical solution of the two-band model and explicit account of the conservation of flux. The conventional estimate is obtained only in limiting cases. In general, the transmission is greater than this estimate, except for carrier energy near a band edge, in which case the transmission goes to zero. Analytical results are obtained for a corrected asymptotic transmission coefficient, and also for the tunneling current density using the conventional estimate of the transmission coefficient. (c) 2006 Elsevier Ltd. All rights reserved.