We have studied single-stranded DNA translocation through a semiconductor membrane consisting of doped p and n layers of Si forming a p-n-junction. Using Brownian dynamics simulations of the biomolecule in the self-consistent membrane-electrolyte potential obtained from the Poisson-Nernst-Planck model, we show that while polymer length is extended more than when its motion is constricted only by the physical confinement of the nanopore. The biomolecule elongation is particularly dramatic on the n-side of the membrane where the lateral membrane electric field restricts (focuses) the biomolecule motion more than on the p-side. The latter effect makes our membrane a solid-state analog of the α-hemolysin biochannel. The results indicate that the tunable local electric field inside the membrane can effectively control dynamics of a DNA in the channel to either momentarily trap, slow down or allow the biomolecule to translocate at will.