A UV‐preionized rare‐gas halide laser with a large aperture to 7×7 cm2and active volume of 4lhas been operated at a high pressure regime of 5 atm. Beam profile measurements at the midplane between electrodes have shown the beam widths of 7 cm at a half‐energy density both in KrF and XeCl. The improvement in discharge homogeneity and extension of the optical pulse duration have been obtained by the peaking of the discharge current with a small stray capacitance between the rail gap and the laser head as well as by the use of Ne rather than He as a buffer gas, resulting in the output energy of 13.8 J in XeCl and 5.0 J in KrF.