  We demonstrate that X-ray irradiation can be used to induce an
insulator-metal transition in Si-doped Al$_{0.35}$Ga$_{0.65}$As, a
semiconductor with {\it DX} centers. The excitation mechanism of the {\it DX}
centers into their shallow donor state was revealed by studying the
photoconductance along with fluorescence. The photoconductance as a function of
incident X-ray energy exhibits an edge both at the Ga and As K-edge, implying
that core-hole excitation of Ga and As are efficient primary steps for the
excitation of {\it DX} centers. A high quantum yield ($\gg 1$) suggests that
the excitation is indirect and nonlocal, due to secondary electrons, holes, and
fluorescence photons.
