Intermetallic compounds with semiconducting properties are rare, but they give rise to advanced materials for energy conversion and saving applications. Here, we present ReGa2Ge, a new electron-precise narrow-gap intermetallic semiconductor. The compound crystallizes in the IrIn3 structure type (space group P4(2)/mnm, a = 6.5734(3) angstrom, c = 6.7450(8) angstrom, and Z = 4), where Re atoms occupy the Ir site, while Ga and Ge jointly populate the In sites. Ga-69,Ga-71 nuclear quadrupole resonance spectroscopy indicates nonstatistical partially ordered distribution of Ga and Ge over two available crystallographic sites; however, the Ga:Ge ratio is exactly 2:1 without noticeable homogeneity range. The stoichiometry of ReGa2Ge ensures its precise valence electron count, which is 17 e(-) per formula unit. Accordingly, a narrow energy gap opens up at the Fermi energy in the electronic structure. Electrical resistivity, Seebeck coefficient, and thermal conductivity are in agreement with the semiconducting behavior deduced from the electronic structure calculations and point to prospective thermoelectric properties at high temperatures. Bonding analysis reveals dominant covalency in Re-E (E = Ga, Ge) and Re-Re interactions.