The dependence of output energy and efficiency of the electric-discharge ArF (193 nm) and KrF (248 nm) excimer lasers on the geometry of active medium and parameters of a high-voltage excitation has been investigated. The design and parameters of the discharge chamber and of the high-voltage excitation circuit of the LC inverter type with automatic preionization (API) providing for the specific pump power of 3.5 MW/cm3 as high were developed and optimized. In a gas active mixture He:Ar:F2 = 79.7:20:0.3 at the total pressure of 2.2 atm, we have managed to achieve, for the first time, the 850 mJ as high output energy of the ArF laser at the over-all efficiency of 1.7% and the pulse duration (FWHM) of 15 ± 1 ns. For a KrF laser in the gas mixture of He:Ne:Kr:F2 = 44.9:44.9:10:0.2 at the total pressure of 2.8 atm, the plug-in efficiency of 2.5% with output radiation energy of 840 mJ was achieved. The maximum output energy of the KrF laser was 1.15 J at the over-all efficiency of 2.2%, pulse duration (FWHM) of 24 ± 1 ns, and the pulse power up to 48 MW.