[en] We have performed large-scale configuration interaction (CI) calculations using CIV3for the lowest (in energy) 155 fine-structure levels of aluminum-like germanium ion. We have calculated the energies and lifetimes of these levels, together with oscillator strengths, and transition probabilities for the electric-dipole (optically allowed and intercombination) transitions among the levels of ground state 3s"23p ("2P) and higher energy levels of states 3s3p"2, 3s"23d, 3p"3, 3s3p3d, 3p"23d, 3s3d"2,3p3d"2, 3d"3,3s"2 (4s, 4p, 4d, 4f) of Ge XX in the LSJ coupling scheme. The present results include relativistic effects through the Breit–Pauli operator. Improvements to the ab initio calculations are made by applying a “fine-tuning” technique in which small adjustments are made to some diagonal elements of the Hamiltonian matrix so as to bring the calculated energy separations into as close agreement as possible with experimental values. Comparisons are made with other available experimental and theoretical results and the accuracy of the present results is assessed. - Highlights: • New atomic data for Ge XX. • Configuration interaction calculation. • Relativistic effects introduced via the Breit–Pauli approximation. • All energy levels within the n=3 complex, plus 3s"24l levels. • Oscillator strengths of transitions between these levels.